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.

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"
        }
    }
}

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
    }
}