Denodo OData 2.0 Service - User Manual

Last modified on: 08 May 2020

Overview

OData (Open Data Protocol) is a REST-based protocol for querying and updating data using simple HTTP messages. It is an OASIS standard based on technologies such as HTTP, Atom/XML and JSON.

Denodo OData Service allows Denodo users to connect to the Denodo Platform and query its databases using an OData 2.0 interface.

Note that this document will use <VERSION> as a placeholder for the specific version of the Denodo Platform you are installing the Denodo OData Service for. So this placeholder should be replaced by the Denodo version number of your installation.

Installation

The Denodo OData Service distribution consists of:

A war file: denodo-odata2-service-<VERSION>.war

A documentation folder containing this user manual

A scripts folder containing the scripts to install the service into tomcat embedded

For running the Denodo OData Service you need to deploy the war file in Apache Tomcat 7+ (using Java 7 or later). You need to include the Virtual DataPort (VDP) driver in the folder /lib of Apache Tomcat 7+.

VDP driver (denodo-vdp-jdbcdriver.jar) is in the folder:

$DENODO_HOME\tools\client-drivers\jdbc in Denodo Platform 6.0 and later

$DENODO_HOME\lib\vdp-jdbcdriver-core in Denodo Platform 5.5

The web application container must provide the data source configuration in order to connect to the Denodo Virtual DataPort server using JNDI. The JNDI name of the resource must be jdbc/VDPdatabase. See the Configuring JNDI resources in Apache Tomcat for more information.

The Denodo OData service has some properties:

odataserver.address service name, /denodo-odata.svc by default.

odataserver.serviceRoot root URI of the service. It is an optional property, empty by default. It should be configured when the OData service is going to be accessed through a gateway, so links within the OData response use this URI as root.

For example, being:

odataserver.serviceRoot=https://gw.denodo.com:9000/ODATA/

and accessing:

http://server001:9090/denodo-odata2-service-<VERSION>/denodo-odata.svc/movies

will return this kind of URI within the response:

https://gw.denodo.com:9000/ODATA/denodo-odata.svc/movies

server.pageSize default number of returned entries per request (see Pagination section for more information)

enable.adminUser boolean value that allows you to deny access to the OData service using the admin user if the specified value is false.

disable.basicAuthentication: true if the access to the OData service is not allowed using HTTP Basic authentication. Note that if this property is set to true, OAuth 2.0 authentication (only available for Denodo Platform 7.0 and later) has to be available.

disable.oauth2Authentication: true if the access to the OData service is not allowed using OAuth 2.0 authentication. Note that this property is only available for Denodo Platform 7.0 and later and if it is set to true, Basic authentication has to be available.

debug.enabled: true for support purposes. With this property enabled the service response contains additional helpful data. It is false by default.

The war file includes a configuration file WEB-INF/classes/configuration.properties that has default values for the properties explained above:

odataserver.address=/denodo-odata.svc

odataserver.serviceRoot=

server.pageSize=1000

enable.adminUser=true

debug.enabled=false

Besides, these properties can be provided by the web container via JNDI (see the Configuring JNDI resources in Apache Tomcat section for more information).

Properties configured at the web container as JNDI entries have higher precedence than those established at the configuration.properties file.

Once you deploy the war you can use the Denodo OData Service from a web client, using HTTP Basic Authentication with VDP-valid credentials. Therefore you may use URLs that are of the form:

http://localhost:8080/denodo-odata.svc/<DBNAME>

Note that for the sake of simplicity in this document, we will consider the OData server to be installed at the ROOT context of the web server.

Deploying into the Denodo embedded web container

For deploying the service in the internal web container of the Denodo Platform you have two options:

with the option A you can execute manually the scripts

with the option B, you can run the start and the stop of the application as a Service in Windows NT/2000/2003/XP/Vista.

Option A

You should follow these steps:

Copy the denodo-odata2-service-<VERSION>.war into <DENODO_HOME>/resources/apache-tomcat/webapps/

Create a context xml file for the service. You can use the xml file in the Denodo OData Service distribution as a template: /scripts/denodo-odata2-service-<VERSION>.xml.
Copy the denodo-odata2-service-<VERSION>.xml file into <DENODO_HOME>/resources/apache-tomcat/conf/DenodoPlatform-<VERSION>/localhost

Check in <DENODO_HOME>/resources/apache-tomcat/conf/catalina.properties

file that the common.loader property (shared.loader in Denodo 5.5) includes a reference to the VDP JDBC Driver.

If missing, add it:

${catalina.base}/../../tools/client-drivers/jdbc/denodo-vdp-jdbcdriver.jar for Denodo Platform 7.0 and later

${catalina.base}/../../tools/client-drivers/jdbc/denodo-vdp-jdbcdriver-basic.jar for Denodo Platform 6.0

${catalina.base}/../../lib/vdp-jdbcdriver-core/denodo-vdp-jdbcdriver-basic.jar for Denodo Platform 5.5

Create launch scripts for the service. You can use as a template the files located at the scripts folder in the Denodo OData Service distribution:

odata_service_startup.bat(.sh)

odata_service_shutdown.bat(.sh)

Make sure to modify the DENODO_HOME variable in the script templates to point to your Denodo installation.

Copy the launch scripts into <DENODO_HOME>/bin.

Configure via JNDI the VDP data source and those properties you want to change their default value (see the Configuring JNDI resources in Apache Tomcat for more information).

Run the <DENODO_HOME>/bin/odata_service_startup.bat(.sh) script and navigate to:

http://localhost:9090/denodo-odata2-service-<VERSION>/denodo-odata.svc/<DBNAME>

Option B

This option is only for Windows systems.

Same as option A

Create service script for the Denodo Odata Service (odata2_service_service). You can use the attached template. Make sure to modify the DENODO_HOME variable in the script templates to point to your Denodo installation.

Create the file service.conf and copy in the folder <DENODO_HOME>/conf/denodo-odata2-service-service/, you can use the attached template. Make sure to modify the DENODO_HOME variable in the script templates to point to your Denodo installation.

Install as a Windows service. Execute odata2-service-service.bat install

You can manage the installed service from the application of Windows: Services.

After launching of the service you can navigate to:

http://localhost:9090/denodo-odata2-service-<VERSION>/denodo-odata.svc/<DBNAME>

Configuring JNDI resources in Apache Tomcat

Data source configuration

For Denodo Platform 6.0 and later

Declare the data source with the name jdbc/VDPdatabase in Apache Tomcat’s server.xml file.

If you deploy the Denodo OData Service into the Denodo embedded web container you must declare the JNDI resource in:

<DENODO_HOME>/resources/apache-tomcat/conf/server.xml file

Below, there is an example:

<Resource name="jdbc/VDPdatabase"

auth="Container"

type="javax.sql.DataSource"

username="admin" password="admin"

url="jdbc:vdb://localhost:9999/admin"

driverClassName="com.denodo.vdp.jdbc.Driver"

initialSize="5"

maxWaitMillis="5000"

maxTotal="20"

maxIdle="5"

validationQuery="select 1"

poolPreparedStatements="true"/>

</GlobalNamingResources>

Reference the JNDI resource from Apache Tomcat’s context.xml file.

If you deploy the Denodo OData service into the Denodo embedded web container the context.xml file is in the <DENODO_HOME>/resources/apache-tomcat/conf folder.

<ResourceLink name="jdbc/VDPdatabase"

global="jdbc/VDPdatabase"

type="javax.sql.DataSource"/>

</Context>

For Denodo Platform 5.5

Declare the data source with the name jdbc/VDPdatabase in Apache Tomcat’s context.xml file.

If you deploy the Denodo OData Service into the Denodo embedded web container you must declare the JNDI resource in:

<DENODO_HOME>/resources/apache-tomcat/conf/context.xml file

<Resource name="jdbc/VDPdatabase"

auth="Container"

type="javax.sql.DataSource"

username="admin" password="admin"

url="jdbc:vdb://localhost:9999/admin"

driverClassName="com.denodo.vdp.jdbc.Driver"

initialSize="5"

maxWaitMillis="5000"

maxWait="5000"

maxTotal="20"

maxActive="20"

maxIdle="5"

minIdle="0"

validationQuery="select 1"

poolPreparedStatements="true"/>

</Context>

* The settings described for Denodo Platform 6.0 can work with 5.5 but in the initialization of Tomcat embedded would appear a spurious error that you could ignore.

* The parameter minIdle could be greater than 0. In this way the performance of the connections would be better, but other applications could maintain open connections that never will be used.

Properties configuration

Declare the properties values in the context.xml file:

<Environment type="java.lang.String"

name="odataserver.address"

value="/denodo-odata.svc"/>

<Environment type="java.lang.String"

name="odataserver.serviceRoot"

value=""/>

<Environment type="java.lang.Integer" name="server.pageSize"

value="1000"/>

<Environment type="java.lang.Boolean" name="enable.adminUser"

value="false"/>

<Environment type="java.lang.Boolean"

name="debug.enabled" value="false"/>

</Context>

If you deploy the service in the internal web container of the Denodo Platform, this file is at <DENODO_HOME>/resources/apache-tomcat/conf.

Virtual DataPort Privilege Requirements

Users of OData Service should have the following VDP privileges assigned:

At database level

Connect

At view level

Metadata for Denodo Platform 6.0 and later

Read: If you do not have Read access to an entire database, but you have it over some of its elements, the OData Service will only list the elements that you have Read privilege over. / Execute: for Denodo Platform 7.0 and later as the privilege Read has been renamed to Execute

Features

Denodo OData Service provides the following main features:

Read-only access to Denodo databases:

Metadata
Entities
Items of an entity
Properties of an item
Property values
Relationships between entities

Format results in AtomPub and JSON

Query options

$select
$filter
$expand
$orderby
$skip
$top
$inlinecount

Pagination

HTTP Authentication

Basic
OAuth 2.0 (only available for Denodo Platform 7.0 and later)

Serving Metadata

There are two types of metadata documents:

The Service Document lists all the entities offered by the data service.

It is available at the root URI of the service, specifying the database name where we are going to get information: /denodo-odata.svc/<DBNAME>.

Below, there is an example where the accessible collections of movies database are actor, address, city, country, film and film_actor.

http://localhost:8080/denodo-odata.svc/movies

<?xml version='1.0' encoding='utf-8'?>

<atom:title>Default</atom:title>

<atom:title>actor</atom:title>

</collection>

<atom:title>address</atom:title>

</collection>

<atom:title>city</atom:title>

</collection>

<atom:title>country</atom:title>

</collection>

<atom:title>film</atom:title>

</collection>

<atom:title>film_actor</atom:title>

</collection>

</workspace>

</service>

The Service Metadata Document, also called Entity Data Model (EDM), is an XML representation of the data model exposed by the service. It is available at .../$metadata:

http://localhost:8080/denodo-odata.svc/movies/$metadata

Example of association that represents a relationship between country and city. Every country element is related with zero or more city elements:

<Summary>Association between cities and countries</Summary>

</Documentation>

<End Type="com.denodo.odata2.country" Multiplicity="1"

Role="country"/>

<End Type="com.denodo.odata2.city" Multiplicity="*"

Role="cities"/>

</Principal>

</Dependent>

</ReferentialConstraint>

</Association>

The Denodo OData Service maps these OData structures to VDP concepts like this:

Denodo ODATA Service	VDP
Entity Type	View Definition
Entity Type > Property	View Column
Entity Type > Navigation Property	Association Role
Association	Association Definition
Entity Set	View Data
Association Set	(Associated data)
Imported Functions	-

Querying Data: The Basics

Querying collections

In the Service Metadata Document (see the Metadata section for more information) you can see the entity set names and to see its data you must use the following URL:

/denodo-odata.svc/<DBNAME>/collectionName

Example:

/denodo-odata.svc/movies/actor

Note that, for the sake of simplicity, we are removing the server and port from the examples.

Obtaining items by primary key

Each item could be identified using its primary key property:

denodo-odata.svc/<DBNAME>/collectionName(keyvalue)

Examples:

/denodo-odata.svc/movies/actor(1)

/denodo-odata.svc/movies/store_category('F0')

The primary key can be a compound key, and in this case you must include all values separated by commas:

/denodo-odata.svc/<DBNAME>/collectionName(key1,key2)

Example:

/denodo-odata.svc/movies/film_actor(actor_id=1,film_id=1)

Accessing individual properties

Properties of an entry can be accessed individually:

/denodo-odata.svc/<DBNAME>/collectionName(key)/propertyName

Example:

/denodo-odata.svc/movies/actor(1)/first_name

Response:

{

"d": {

"first_name": "PENELOPE"

}

Accessing individual property values

The value of a property is available as a raw value:

/denodo-odata.svc/<DBNAME>/collectionName(key)/propertyName/$value

Example:

/denodo-odata.svc/movies/actor(1)/first_name/$value

Response:

PENELOPE

Accessing complex properties

Properties can be complex but they are also accessible. You must point out the property path, from the complex to the simple one:

/denodo-odata.svc/<DBNAME>/collectionName(pk)/propName/complexProp/propName

For example, for the following film_data complex field in a struct_table_film entity:

"table_id": "1",

"film_data": {

"__metadata": {

"type": "com.denodo.odata2.struct_table_film_film_data"

"id": "1",

"title": "ACADEMY DINOSAUR",

"description": "ELIZABETH"

}

we could perform the following call:

/denodo-odata.svc/movies/struct_table_film(1)/film_data/title

Response:

{

"d": {

"title": "ACADEMY DINOSAUR"

}

Counting elements in a collection: $count

If you want to know the number of elements (entries) in a collection you have to add $count to the URL:

/denodo-odata.svc/<DBNAME>/collectionName/$count

Example:

/denodo-odata.svc/movies/actor/$count

Response:

200

Establishing response format

OData resources can be represented in AtomPub (XML) or JSON, being AtomPub the default format.

Clients can request the format through the system query option $format or through the Accept header. In the case that both the Accept header and the $format query option are specified on a request, the $format query option has a higher precedence.

The example URLs below will show the same data but represented using the AtomPub format as defined in OData:Atom in the first one and in the second using the JSON format as defined in OData:JSON.

/denodo-odata.svc/movies/actor?$format=atom

/denodo-odata.svc/movies/actor?$format=json

Alternatively, this format can be requested using the HTTP header Accept:

Accept: application/json

Navigating Associations

Publishing VDP Associations through OData

Denodo Virtual DataPort allows you to define relationships between the elements of two views. The following example shows an association where the elements of the country view can be related with the elements of the city view. Every country is related with zero or more cities.

The association can be seen in the Service Metadata Document:

</Documentation>

</Principal>

</Dependent>

</ReferentialConstraint>

</Association>

Querying related entries

Denodo OData Service allows navigating the associations defined in VDP in order to get all the entities related with a particular entity. This is done by means of navigation properties.

/denodo-odata.svc/<DBNAME>/collectionName(key)/navigationPropertyName

For example, being cities a navigation property in the entity type country that navigates towards the city entity type:

/denodo-odata.svc/movies/country(1)/cities

Response:

{

"d": {

"results": [

{

"__metadata": {

"id": "http://localhost:8080/denodo-odata.svc/movies/city(251)",

"uri": "http://localhost:8080/denodo-odata.svc/movies/city(251)",

"type": "com.denodo.odata2.city"

"city_id": 251,

"city": "Kabul",

"country_id": 1,

"last_update": "\\/Date(1139975125000+0060)\\/",

"country": {

"__deferred": {

"uri": "http://localhost:8080/denodo-odata.svc/movies/city(251)/country"

}

} } ] } }

Lists of links between entries

You can get the links to the collection of entries relationed with one in particular:

/denodo-odata.svc/<DBNAME>/collectionName(key)/$links/navProp

The URL specified above will show all the URLs which allows the access to every entry associated with the entry collectionName(key) through the navigation property navProp.

Example:

/denodo-odata.svc/movies/country(2)/$links/cities

Response:

{

"d": [

{

"uri": "http://localhost:8080/denodo-odata.svc/movies/city(59)"

{

"uri": "http://localhost:8080/denodo-odata.svc/movies/city(63)"

{

"uri": "http://localhost:8080/denodo-odata.svc/movies/city(483)"

}

]

}

Advanced Querying

OData defines some query options that allows refining the requests: $filter, $select, $orderby and $expand.

Selection: $filter

A URI with a $filter system query option identifies a subset of the entries from the collection that satisfy the $filter predicate expression.

Expressions can reference properties and literals. The latter can be strings (enclosed in single quotes), the null literal, numbers or boolean values.

Denodo OData service supports the following operations and functions:

Operators

Operator	Description	Example
eq	Equal	/actor?$filter=first_name eq 'GRACE'
ne	Not equal	/actor?$filter=first_name ne 'GRACE'
gt	Greater than	/actor?$filter=actor_id gt 5
ge	Greater than or equal	/actor?$filter=actor_id ge 5
lt	Less than	/actor?$filter=actor_id lt 10
le	Less than or equal	/actor?$filter=actor_id le 10
and	Logical and	/actor?$filter=actor_id gt 5 and actor_id lt 10
or	Logical or	/actor?$filter=actor_id lt 5 or first_name eq 'GRACE'
not	Logical negation	/actor?$filter=not (actor_id eq 1)

String functions

The following functions are available for strings operations:

substringof(string p0, string p1) returns true when the value of the property name specified in p1 contains the string p0. Otherwise returns false.

startswith(string p0, string p1) returns true when the value of the property name specified in p0 starts with the string p1. Otherwise returns false.

endswith(string p0, string p1) returns true when the value of the property name specified in p0 ends with the string p1. Otherwise returns false.

indexof(string p0, string p1) returns the position of the string p1 in the value of the property name specified in p0.

length(p0) returns the length of the value of the property name specified in p0.

substring(string p0, int pos) returns a new string that is a substring of the value of the property name specified in p0. The substring begins with the character at the specified pos and extends to the end of this string.

substring(string p0, int pos, int length) returns a new string that is a substring of the value of the property name specified in p0. The substring begins at the specified pos and extends to the character at index pos + length.

tolower(string p0) returns a copy of the value of the property name specified in p0 converted to lowercase.

toupper(string p0) returns a copy of the value of the property name specified in p0 converted to uppercase.

trim(string p0) returns a copy of the value of the property name specified in p0 with leading and trailing whitespace omitted.

concat(string p0, string p1) returns a new string that is a concatenation of the string p0 and the string p1.

The following table shows a summary and examples of this functions:

Function	Example
bool substringof(string p0, string p1)	/actor?$filter=substringof('LO', first_name) eq true
bool startswith(string p0, string p1)	/actor?$filter=startswith(first_name, 'JO') eq true
bool endswith(string p0, string p1)	/actor?$filter=endswith(first_name,'ER') eq true
int indexof(string p0, string p1)	/actor?$filter=indexof(last_name, 'LO') eq 3
int length(string p0)	/actor?$filter=length(first_name) eq 4
string substring(string p0, int pos)	/actor?$filter=substring(first_name, 2) eq 'RO'
string substring(string p0, int pos, int length)	/actor?$filter=substring(first_name, 2,3) eq 'TTH'
string tolower(string p0)	/actor?$filter=tolower(first_name) eq 'nick'
string toupper(string p0)	/actor?$filter=toupper(first_name) eq 'NICK'
string trim(string p0)	/actor?$filter=trim(first_name) eq 'JENNIFER'
string concat(string p0, string p1)	/actor?$filter=concat( concat(first_name,', '), last_name) eq 'JENNIFER, DAVIS'

Math functions

There are three math functions: round, floor, ceiling. Each one allows Double or Decimal types as parameters and the returned value is of the same type as the parameter.

Function	Example
double round(double p0)	/film?$filter=round(replacement_cost) eq 21
decimal round(decimal p0)	/film?$filter=round(rental_rate) eq 1
double floor(double p0)	/film?$filter=floor(replacement_cost) eq 20
decimal floor(decimal p0)	/film?$filter=floor(rental_rate) eq 0
double ceiling(double p0)	/film?$filter=ceiling(replacement_cost) eq 21
decimal ceiling(decimal p0)	/film?$filter=ceiling(rental_rate) eq 1

Date functions

Function	Example
int hour(DateTime p0)	/actor?$filter=hour(last_update) eq 3
int minute(DateTime p0)	/actor?$filter=minute(last_update) eq 34
int second(DateTime p0)	/actor?$filter=second(last_update) eq 33

Projection: $select

The $select system query option returns only the properties explicitly requested.

$select expression can be a comma-separated lists of properties or the star operator (*), which will retrieve all the properties.

Example:

/denodo-odata.svc/movies/actor?$select=actor_id,first_name,last_name

Response:

…

{

"__metadata": {

"id": "http://localhost:8080/denodo-odata.svc/movies/actor(1)",

"uri": "http://localhost:8080/denodo-odata.svc/movies/actor(1)",

"type": "com.denodo.odata2.actor"

"actor_id": 1,

"first_name": "PENELOPE",

"last_name": "GUINESS"

…

Another example:

/denodo-odata.svc/movies/actor?$select=*

Response:

…

{

"__metadata": {

"id": "http://localhost:8080/denodo-odata.svc/movies/actor(1)",

"uri": "http://localhost:8080/denodo-odata.svc/movies/actor(1)",

"type": "com.denodo.odata2.actor"

"actor_id": 1,

"first_name": "PENELOPE",

"last_name": "GUINESS",

"last_update": "\\/Date(1139974473000+0060)\\/"

…

Ordering results: $orderby

The $orderby query string option specifies the order in which items are returned:

/denodo-odata.svc/<DBNAME>/collectionName?$orderby=attribute [asc|desc]

To order the collection the resource path must identify a collection of entries, otherwise this option is unavailable.

The keywords asc and desc determine the direction of the sort (ascending or descending, respectively). If asc or desc are not specified items are returned in ascending order. Null values come before non-null values when sorting in ascending order and vice versa.

You can also sort by multiple attributes:

/denodo-odata.svc/<DBNAME>/collectionName?$orderby=attribute1[asc|desc],attribute2 [asc|desc]

Example:

/denodo-odata.svc/movies/address?$orderby=zip,client_identifier desc

Including related resources: $expand

$expand is available since Denodo Platform 6.0.

An $expand expression is a comma-separated list of navigation properties that specifies the related entities that should be represented inline.

Example:

/denodo-odata.svc/movies/country?$expand=cities

Response:

…

"__metadata": {

"id": "http://localhost:8080/denodo-odata.svc/admin/country(1)",

"uri": "http://localhost:8080/denodo-odata.svc/admin/country(1)",

"type": "com.denodo.odata2.country"

"country_id": 1,

"country": "Afghanistan",

"last_update": "/Date(1140007440000+0060)/",

"cities": {

"results": [

{

"__metadata": {

"id": "http://localhost:8080/denodo-odata.svc/admin/city(251)",

"uri": "http://localhost:8080/denodo-odata.svc/admin/city(251)",

"type": "com.denodo.odata2.city"

"city_id": 251,

"city": "Kabul",

"country_id": 1,

"last_update": "/Date(1140007525000+0060)/",

"country": {

"__deferred": {

"uri":

"http://localhost:8080/denodo-odata.svc/admin/city(251)/country"

}

]

}

…

The following is an example with two navigation properties. This URI identifies the film set as well as the film_actor (actors is the navigation property) and the film_category (categories is the navigation property) associated with each film:

/denodo-odata.svc/movies/film?$expand=film_actor,film_categories

Response:

...

"__metadata": {

"id": "http://localhost:8080/denodo-odata.svc/admin/film(1)",

"uri": "http://localhost:8080/denodo-odata.svc/admin/film(1)",

"type": "com.denodo.odata2.film"

"film_id": 1,

"title": "ACADEMY DINOSAUR",

"description": "A Epic Drama of a Feminist And a Mad Scientist who must Battle a Teacher in The Canadian Rockies",

"release_year": "/Date(1136106000000+0060)/",

"language_id": 1,

"original_language_id": null,

"rental_duration": 6,

"rental_rate": "0.99",

"length": 86,

"replacement_cost": "20.99",

"rating": "PG",

"special_features": "Deleted Scenes,Behind the Scenes",

"last_update": "/Date(1140008622000+0060)/",

"film_actor": {

"results": [

{

"__metadata": {

"id":

"http://localhost:8080/denodo-odata.svc/admin/film_actor(actor_id

1,film_id=1)",

"uri":

"http://localhost:8080/denodo-odata.svc/admin/film_actor(actor_id

1,film_id=1)",

"type": "com.denodo.odata2.film_actor"

"actor_id": 1,

"film_id": 1,

"last_update": "/Date(1140008703000+0060)/",

"actor_role": {

"__deferred": {

"uri":

"http://localhost:8080/denodo-odata.svc/admin/film_actor(actor_id

1,film_id=1)/actor_role"

}

...

"film_categories": {

"results": [

{

"__metadata": {

"id":

"http://localhost:8080/denodo-odata.svc/admin/film_category(film_

d=1,category_id=6)",

"uri":

"http://localhost:8080/denodo-odata.svc/admin/film_category(film_

d=1,category_id=6)",

"type": "com.denodo.odata2.film_category"

"film_id": 1,

"category_id": 6,

"last_update": "/Date(1140008829000+0060)/",

"film": {

"__deferred": {

"uri":

"http://localhost:8080/denodo-odata.svc/admin/film_category(film_

d=1,category_id=6)/film"

}

]

}

...

Example with a multi-level relationship. This URI identifies the film set as well as each of the film_actor associated with each film. In addition, it also identifies the actors associated with each film_actor:

/denodo-odata.svc/movies/film?$expand=film_actor/actor

Response:

"__metadata": {

"id": "http://localhost:8080/denodo-odata.svc/admin/film(1)",

"uri": "http://localhost:8080/denodo-odata.svc/admin/film(1)",

"type": "com.denodo.odata2.film"

"film_id": 1,

"title": "ACADEMY DINOSAUR",

"description": "A Epic Drama of a Feminist And a Mad Scientist who must Battle a Teacher in The Canadian Rockies",

"release_year": "/Date(1136073600000+0060)/",

"language_id": 1,

"original_language_id": null,

"rental_duration": 6,

"rental_rate": "0.99",

"length": 86,

"replacement_cost": "20.99",

"rating": "PG",

"special_features": "Deleted Scenes,Behind the Scenes",

"last_update": "/Date(1140008622000+0060)/",

"film_actor": {

"results": [

{

"__metadata": {

"id":

"http://localhost:8080/denodo-odata.svc/admin/film_actor(actor_id

1,film_id=1)",

"uri":

"http://localhost:8080/denodo-odata.svc/admin/film_actor(actor_id

1,film_id=1)",

"type": "com.denodo.odata2.film_actor"

"actor_id": 1,

"film_id": 1,

"last_update": "/Date(1140008703000+0060)/",

"actor": {

"__metadata": {

"id":

"http://localhost:8080/denodo-odata.svc/admin/actor(1)",

"uri":

"http://localhost:8080/denodo-odata.svc/admin/actor(1)",

"type": "com.denodo.odata2.actor"

"actor_id": 1,

"first_name": "PENELOPE",

"last_name": "GUINESS",

"last_update": "/Date(1140006873000+0060)/",

"film_actor": {

"__deferred": {

"uri":

"http://localhost:8080/denodo-odata.svc/admin/actor(1)/film_actor"

}

"film": {

"__deferred": {

"uri":

"http://localhost:8080/denodo-odata.svc/admin/film_actor(actor_id

1,film_id=1)/film"

}

…

Specifying maximum number of results: $top

With the $top option you can select the n first entries of the collection, being n a non-negative integer:

/denodo-odata.svc/<DBNAME>/collectionName?$top=n

Note that n is a positive integer, a negative value means that the URL is malformed.

Example:

/denodo-odata.svc/movies/address?$top=1

Response:

{

"d": {

"results": [

{

"__metadata": {

"id":

"http://localhost:8080/denodo-odata.svc/movies/address('C001')",

"uri":

"http://localhost:8080/denodo-odata.svc/movies/address('C001')",

"type": "com.denodo.odata2.address"

"client_identifier": "C001",

"street": "3989 Middlefield Rd",

"city": "San Jose",

"zip": "94085",

"state": "CA",

"primary_phone": "(408) 813-9318",

"country": "UNITED STATES"

}

]

}

Specifying offset: $skip

With the option $skip, the n first entries of the collection will not be shown in the response. n is a non-negative integer.

denodo-odata.svc/<DBNAME>/collectionName?$skip=n

Example:

/denodo-odata.svc/movies/address?$skip=79

Response:

{

"d": {

"results": [

{

"__metadata": {

"id":

"http://localhost:8080/denodo-odata.svc/movies/address('C080')",

"uri":

"http://localhost:8080/denodo-odata.svc/movies/address('C080')",

"type": "com.denodo.odata2.address"

"client_identifier": "C080",

"street": "2347 Santa Ana St",

"city": "Palo Alto",

"zip": "94303-3141",

"state": "CA",

"primary_phone": "(650) 856-9738",

"country": "UNITED STATES"

}

]

}

Asking for total result count: $inlinecount

The number of entries in a collection identified by the resource path section of the URI may be added to the data shown in the response using the $inlinecount system query option. This option allow two possible values:

allpages the OData server include a count of number of entities in the collection identified by the URI.
none the OData server do not include a count in the response. This option is equivalent to a URI without the $inlinecount option.

Note that the count is calculated after applying any $filter system query options present in the URI.

Examples:

/denodo-odata.svc/movies/actor?$inlinecount=allpages

Response:

{

"d": {

"__count": "200",

"results": [

…

]

}

Another example:

/denodo-odata.svc/movies/actor?$inlinecount=allpages&$filter=actor_id eq 1

Response:

{

"d": {

"__count": "1",

"results": [

{

"__metadata": {

"id": "http://localhost:8080/denodo-odata.svc/movies/actor(1)",

"uri": "http://localhost:8080/denodo-odata.svc/movies/actor(1)",

"type": "com.denodo.odata2.actor"

"actor_id": 1,

"first_name": "PENELOPE",

"last_name": "GUINESS",

"last_update": "\\/Date(1139974473000+0060)\\/"

}

]

}

Another example:

/denodo-odata.svc/movies/actor?$inlinecount=none

Response:

Actor data, just like without $inlinecount option.

Pagination

Whenever the Denodo OData Service has to return a collection of entries which size exceeds that configured at the server.pageSize property of its configuration file, it will split the response into pages, returning only the first 1000 entries (the default value for page size).

Denodo OData Service will add to the response a next link, which will easily allow the client to request the next page of results.

Next links include a $skiptoken parameter. They look like this:

/denodo-odata.svc/movies/actor?$skiptoken=1

If the original request includes query options, the result will show the next link with these query options and a $skiptoken as in the examples below.

Example request:

/denodo-odata.svc/movies/actor?$top=2

Response:

...

"__next":

"http://localhost:8080/denodo-odata.svc/movies/actor?$top=2&$skiptoken=1"

...

Debug Option

For debug purposes there is a possibility to enrich the OData service response with additional helpful data.

The additional data consists of information about the request, the response, the parsed request URI, the server environment, library timings, and the stack trace in case an error occurred.

To request the debug output for a request to the OData service the query parameter odata-debug=json or odata-debug=html must be appended to the original request URL:

http://localhost:8080/denodo-odata.svc/movies/?odata-debug=json

Limitations

Read-only access

The access to Denodo databases via this Denodo OData Service is read-only.

Representing arrays

OData 2.0 does not support Collections/Bags/Lists that will allow us to give support to arrays as complex objects. Now they are displayed between square brackets as a comma-separated list of values.

Unavailable operators in the $filter system query option

Denodo OData Service does not support arithmetic operators: add (addition), sub (subtraction), mul (multiplication), div (division) and mod (modulo).

Unavailable functions in the $filter system query option

Denodo OData Service does not provide support for the string function replace:

string replace(string p0, string find, string replace)

Denodo OData Service does not provide support for date functions:

int day(DateTime p0)

int month(DateTime p0)

int year(DateTime p0)

Denodo OData Service does not provide support for type functions:

bool isOf(type p0)

bool isOf(expression p0, type p1)

Navigation properties in the $select system query option

Denodo OData Service does not allow navigation properties as selection clauses.

Navigation using complex properties

When there is an association where one of the elements of an end point is a field of a register, Denodo Virtual DataPort does not allow the navigation from the endpoint with the complex property.

Order by using complex properties

Denodo Virtual DataPort does not support the order by clause using fields of registers, therefore the $orderby query string option is not available if you want to sort by a field of a complex property

Limitations in versions prior to Denodo Platform 6.0

Unavailable $expand system query option

This system query option indicates that entries associated with the elements identified by the resource path section must be represented inline.

Counting entries of a collection when there is navigation

Navigational queries does not allow the count(*) function, then if the URL contains a navigation the option of counting entries in a collection ($count) is not available.