MS SQL Server: Filter Based on Fields of Nested Objects
Introduction
You can use the fields of nested objects as well to filter your query results.
For example:
query {
articles(where: { author: { name: { _eq: "Sidney" } } }) {
id
title
}
}
The behavior of the comparison operators depends on whether the nested objects are a single object related via an object relationship or an array of objects related via an array relationship.
- In case of an object relationship, a row will be returned if the single nested object satisfies the defined condition.
- In case of an array relationship, a row will be returned if any of the nested objects satisfy the defined condition.
This is only supported for local relationships, such as relationships between two local database tables. This is not supported for remote relationships, such as remote database relationships or Remote Schema relationships.
Let's look at a few use cases based on the above:
Fetch if the single nested object defined via an object relationship satisfies a condition
Example:
Fetch all articles whose author's name starts with "A":
Fetch if any of the nested objects defined via an array relationship satisfy a condition
Example:
Fetch all authors which have written at least one article which is rated 1:
Fetch if all of the nested objects defined via an array relationship satisfy a condition
By default a row is returned if any of the nested objects satisfy a condition. To achieve the above, we need to frame
the where expression as {_not: {inverse-of-condition}}. This reads as: fetch if not (any of the nested objects
satisfy the inverted condition) i.e. all of the nested objects satisfy the condition.
For example:
| condition | where expression |
|---|---|
{object: {field: {_eq: "value"}}} | {_not: {object: {field: {_neq: "value"}}} |
{object: {field: {_gt: "value"}}} | {_not: {object: {field: {_lte: "value"}}} |
Example:
Fetch all authors which have all of their articles published i.e. have {is_published {_eq: true}.
Fetch if none of the nested objects defined via an array relationship satisfy a condition
By default a row is returned if any of the nested objects satisfy a condition. To achieve the above, we need to frame
the where expression as {_not: {condition}}. This reads as: fetch if not (any of the nested objects satisfy the
condition) i.e. none of the nested objects satisfy the condition.
For example,
| condition | where expression |
|---|---|
{object: {field: {_eq: "value"}}} | {_not: {object: {field: {_eq: "value"}}} |
{object: {field: {_gt: "value"}}} | {_not: {object: {field: {_gt: "value"}}} |
Example:
Fetch all authors which have none of their articles published i.e. have {is_published {_eq: true}:
Fetch if nested object(s) exist/do not exist
You can filter results based on if they have nested objects by checking if any nested objects exist. This can be
achieved by using the expression {} which evaluates to true if any object exists.
Example where nested object(s) exist:
Fetch all authors which have at least one article written by them:
Example where nested object(s) do not exist:
Fetch all authors which have not written any articles:
