Basic Querying¶
This section shows how to query the Denodo GraphQL Service.
Fields¶
GraphQL is about asking for specific fields on objects. Queries can also traverse related objects and their fields, letting users fetch related data in one request.
In the query of the example below, we are requesting the fields
order_id, order_desc and total_price of the object order.
Also, for each order, we are retrieving the related object
order_detail, with its fields prod_id and price.
Query for ‘order’ type fields¶
{
"data": {
"order": [
{
"order_id": 111,
"order_desc": "Internet and phone",
"order_detail": [
{
"prod_id": 2000,
"price": 60
},
{
"prod_id": 2020,
"price": 40
}
],
"total_price": 100
},
{
"order_id": 222,
"order_desc": "Cable at discounted price",
"order_detail": [
{
"prod_id": 2010,
"price": 15
}
],
"total_price": 15
}
]
}
}
Arguments¶
GraphQL allows you to pass arguments to fields to narrow results.
In the query of the example below, we are requesting the fields
order_desc and total_price of the object order that has 222
as order_id.
Query with arguments¶
{
"data": {
"order": [
{
"order_desc": "Cable at discounted price",
"total_price": 15
}
]
}
}
Notice that the following custom scalar types are not supported as an argument in GraphQL queries:
Array
Blob
IntervalDaySecond
IntervalYearMonth
Struct
Xml
Aliases¶
If you want to query for the same fields with different arguments you will need to use aliases to avoid name conflicts.
In the query of the example below, we use first_order and second_order
as aliases of the two queries.
Query with aliases¶
{
"data": {
"first_order": [
{
"order_desc": "Internet and phone",
"total_price": 100
}
],
"second_order": [
{
"order_desc": "Cable at discounted price",
"total_price": 15
}
]
}
}
Fragments¶
Fragments allow you to define a set of fields once and reuse them in all the queries you need, avoiding field repetition.
In the query of the example below, we define the orderFields fragment
and use it in both queries first_order and second_order. This is a
sample, but in complex scenarios fragments are really useful.
Query with fragment¶
{
"data": {
"first_order": [
{
"order_desc": "Internet and phone",
"total_price": 100
}
],
"second_order": [
{
"order_desc": "Cable at discounted price",
"total_price": 15
}
]
}
}
Variables¶
Variables are used when the arguments of a query are going to be dynamic. This way, when we want to use the same query with different argument values, we only have to pass a different variable rather than writing a new GraphQL query.
In the query of the example below, $price is a GraphQL variable.
Query with variables¶
{
"data": {
"order_detail": [
{
"order_id": 333,
"prod_id": 2000,
"last_updated_time": "2018-06-13 17:08:02",
"price": 33
},
{
"order_id": 333,
"prod_id": 2010,
"last_updated_time": "2018-06-13 17:08:02",
"price": 33
}
]
}
}
Directives¶
The Denodo GraphQL Service includes the two directives defined as mandatory in the specification:
@include(if: Boolean): only include this field in the result if the argument is true.@skip(if: Boolean): skip this field if the argument is true.
Query with directive @include¶
{
"data": {
"order": [
{
"order_id": 111,
"order_desc": "Internet and phone"
},
{
"order_id": 222,
"order_desc": "Cable at discounted price"
},
{
"order_id": 333,
"order_desc": "3 in one offer"
}
]
}
}
Pagination¶
Denodo GraphQL Service implements offset-based pagination.
The query order_detail(_offset:1, _first:2) asks for the next two
order_details in the list, skipping the first one.
The pagination arguments are:
_offset: the number of results to skip_first: the number of results to fetch. If_firstis not specified, its value is the one configured in the propertyquery.default-page-sizethat has a default value of1000.
Query with pagination¶
{
"data": {
"order_detail": [
{
"prod_id": 2010,
"price": 33
},
{
"prod_id": 2020,
"price": 33
}
]
}
}