Custom data sources, also called Custom wrappers, are ad-hoc wrappers developed in Java to access any source that Virtual DataPort does not have support for.
These wrappers are developed to expose the metadata and query capabilities of any kind of application or proprietary data repository, to the Denodo Platform.
The section Developing Custom Wrappers of the Developer Guide explains how to develop them.
The Denodo Platform includes the source code of a sample custom source
that retrieves data from Salesforce.com. The example is located at
To compile the classes of the example execute the script
scripts/compile_salesforce_customwrapper, which generates the
You need a Salesforce account to use this sample Custom
source. Before creating the sample custom data source in Virtual
DataPort, you have to import the jar that contains its classes. To do
this, click Jar management on the menu File. Then, click on
Create, select the file
and click Close. When doing this, the contents of the jar are sent
to the Server.
To create a Custom data source, right-click on the Elements Tree and click New > Data source > Custom.
The Tool will display the dialog to create the data source.
The following data are requested in this dialog:
Name. Name of the new data source.
Class name. Full name of the Java class that implements the Custom data source. In our Salesforce example:
If the class you want to use is located in a Jar that was loaded into the Server from the File > Jar management dialog (see section Importing Extensions), select the Select jars check box and then, select the class name from the list.
If the class is inside a jar file that was copied into the
<DENODO_HOME>/extensions/thirdparty/libdirectory, enter the name of the class.
Classpath. Optional. Path to the jar file(s) that contain the Java classes of the custom source.
Although you can use this field, we recommend importing the jar files into the Virtual DataPort server and then, select them in the Select Jars box. That way, you do not depend on these jars being on a particular location.
Leave this field empty if one of these conditions are met:
- You imported the jar file with the “Jar Management” dialog.
- Or the jar file has been copied to the directory
To enter the path, click Browse to select the jar. To select more than one jar, hold Ctrl and select each jar.
When clicking Browse, you will browse the file system of the host where the Server is running and not where the Administration Tool is running.
In our example, leave it empty.
Select Jars. If the class belongs to a jar file imported into the Server, select this check box and select the appropriate Jar in the list below. In our example, select the jar you just have imported.
To select two or more Jars, hold Ctrl and click on the required Jars.
In the Metadata tab, set the folder where the data source will be stored and provide a description.
When editing the data source, you can also change its owner by clicking the button .
Then, click Save to create the data source.
Click Create base view to create a base view over the new data source.
Custom Sources, also called Custom wrappers, may accept input parameters. If they do, you have to provide their value when creating the base view. The Administration Tool will show a suitable component to edit the parameter value depending on its type: a text box, a drop-down list, a check box, etc. The section Developing Custom Wrappers of the Virtual DataPort Developer Guide lists the available types.
If the value of a parameter contains one of the following
characters, you have to escape them with the character
because they are reserved characters in Virtual DataPort:
E.g. if your Salesforce login name is
joe@acme, you have to enter
If you load the value of a parameter with Load file of the “Value
editor”, the Tool automatically escapes these characters. To open this
editor, click on beside the parameter box. This editor is only
available for parameters with the type
We recommend loading the value of a parameter from a file if the value is very long or may contain reserved characters.
If the custom wrapper allows pass-through session credentials it is required to define one input parameter of type “login” and another one of type “password”. If these parameters are present in the custom wrapper, the Administration Tool will show a “Pass-through session credentials” check box to enable this behavior. When executing a view created with this option enabled, the server will use the login and password used by the user to authenticate in the server to fill the login and password parameters of the custom wrapper.
Users should be careful when enabling the cache for views that involve data sources with pass-through credentials enabled. The section Considerations When Configuring Data Sources with Pass-Through Credentials explains the issues that may arise.
The Salesforce wrapper has the following input parameters:
- LOGIN = <your Salesforce.com user name>
- PASSWORD = <your Salesforce.com password>
- TOKEN = <your user token>
- SCHEMA = account (or any other schema available in Salesforce)
The values of the input parameters of the wrapper may affect the schema
of the base views or the behavior of the wrapper. For example, the base
views created over the Salesforce wrapper have different fields
depending on the value of the parameter
SCHEMA. E.g. if the value of
account, the base views will have fields like
billingcity. If the value of
lead, it will have fields like
This feature is very useful to develop Custom sources that can retrieve data from a source and the schema of the data may have different schemas.
Now, click Ok to display the schema that the new base view will have (see New base view from a Custom data source).
At this point, you can change the name of the view and the type of its fields. In the Metadata tab, set the folder where the base view will be stored and provide a description.
Click Save to create the base view.
After creating the base view, you can click on Edit to modify the view. In this dialog, you can rename the fields of the view, change their type and store the view in another folder.
When editing the base view, you can also change its owner by clicking the button .
Using Interpolation Variables as Custom Sources’ Input Parameters¶
When creating a base view over a Custom source that has input parameters, you can provide:
- The values of these parameters.
- Or, interpolation variables.
If you provide interpolation variables, the Tool will ask sample values of these variables in order to query the source and know the schema of the base view. That is because a custom wrapper may return a different schema depending on the value of these parameters.
For example, in the Salesforce wrapper, instead of putting your
credentials in the fields LOGIN and PASSWORD, you can put interpolation
variables. E.g., fill in the field LOGIN with
After creating the base view, you will see that it has two extra fields:
PASSWORD. This fields will be required to query
the view, so they have to be provided in the
WHERE clause of the
When filling in the values of input parameters you can combine several
input variables in the same parameter. E.g. LOGIN =
You can also mix a variable with static text. E.g. LOGIN =
@LOGIN_NAME\@acme.com. In this case, the character
is escaped, so the text
@acme.com is interpreted as a literal.