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Version: v2.x

Metadata API Reference: Computed Fields

Introduction​

computed field is an extra field added to a table, its value is computed via an SQL function which has the table row type as an input argument. Currenty, the Hasura GraphQL engine supports functions returning base types or table row types as computed fields.

Supported from

The metadata API is supported for versions v2.0.0 and above and replaces the older schema/metadata API.

pg_add_computed_field​

pg_add_computed_field is used to define a computed field in a table. There cannot be an existing column or relationship or computed field with the same name.

Create a computed field called full_name on an author table, using an SQL function called author_full_name:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
"type":"pg_add_computed_field",
"args":{
"table":{
"name":"author",
"schema":"public"
},
"source": "default",
"name":"full_name",
"definition":{
"function":{
"name":"author_full_name",
"schema":"public"
},
"table_argument":"author_row"
}
}
}

Args syntax​

KeyRequiredSchemaDescription
tabletrueTableNameName of the table
nametrueComputedFieldNameName of the new computed field
definitiontrueComputedFieldDefinitionThe computed field definition
commentfalseStringCustomise the description shown in GraphQL introspection. If null or omitted then if a comment exists on the database function, it is used as the description, and if not, an autogenerated description is used instead.
sourcefalseSourceNameName of the source database of the table (default: default)

pg_drop_computed_field​

pg_drop_computed_field is used to drop a computed field of a table. If there are other objects dependent on this computed field, like permissions, the request will fail and report the dependencies unless cascade is set to true. If cascade is set to true, the dependent objects are also dropped.

Drop a computed field full_name from a table author:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
"type":"pg_drop_computed_field",
"args":{
"table":{
"name":"author",
"schema":"public"
},
"source": "default",
"name":"full_name",
"cascade": false
}
}

Args syntax​

KeyRequiredSchemaDescription
tabletrueTableNameName of the table
nametrueComputedFieldNameName of the computed field
cascadefalseBooleanWhen set to true, all the dependent items (if any) on this computed fields are also dropped
sourcefalseSourceNameName of the source database of the table (default: default)

bigquery_add_computed_field​

bigquery_add_computed_field is used to define a computed field in a BigQuery table. There cannot be an existing column or relationship or computed field with the same name.

Create a computed field called fetch_articles on an author table, using an SQL function called author_fetch_articles:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
"type":"bigquery_add_computed_field",
"args":{
"table":{
"name":"author",
"dataset":"hasura"
},
"source": "bigquery",
"name":"fetch_articles",
"definition":{
"function":{
"name":"author_fetch_articles",
"dataset":"hasura"
},
"argument_mapping": {
"author_id_arg": "author_id"
},
"return_table": {
"name": "article",
"dataset": "hasura"
}
}
}
}

Args syntax​

KeyRequiredSchemaDescription
tabletrueTableNameName of the table
sourcetrueSourceNameName of the source database of the table
nametrueComputedFieldNameName of the computed field
definitiontrueComputedFieldDefinitionThe computed field definition
commentfalseStringCustomise the description shown in GraphQL introspection. If null or omitted then if a comment exists on the database function, it is used as the description, and if not, an autogenerated description is used instead.

bigquery_drop_computed_field​

bigquery_drop_computed_field is used to drop a computed field of a table in a BigQuery source. If there are other objects dependent on this computed field, like permissions, the request will fail and report the dependencies unless cascade is set to true. If cascade is set to true, the dependent objects are also dropped.

Drop a computed field fetch_articles from a table author:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
"type":"bigquery_drop_computed_field",
"args":{
"table":{
"name":"author",
"dataset":"hasura"
},
"source": "bigquery",
"name":"fetch_articles",
"cascade": false
}
}

Args syntax​

KeyRequiredSchemaDescription
tabletrueTableNameName of the table
sourcetrueSourceNameName of the source database of the table
nametrueComputedFieldNameName of the computed field
cascadefalseBooleanWhen set to true, all the dependent items (if any) on this computed fields are also dropped