Schema/Metadata API Reference: Computed Fields¶

Table of contents

Introduction
add_computed_field
drop_computed_field

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.

add_computed_field¶

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/query HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

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

Args syntax¶

Key	Required	Schema	Description
table	true	TableName	Name of the table
name	true	ComputedFieldName	Name of the new computed field
definition	true	ComputedFieldDefinition	The computed field definition
comment	false	text	comment

ComputedFieldDefinition¶

Key	Required	Schema	Description
function	true	FunctionName	The SQL function
table_argument	false	String	Name of the argument which accepts a table row type. If omitted, the first argument is considered a table argument
session_argument	false	String	Name of the argument which accepts the Hasura session object as a JSON/JSONB value. If omitted, the Hasura session object is not passed to the function

drop_computed_field¶

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/query HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
    "type":"drop_computed_field",
    "args":{
        "table":{
            "name":"author",
            "schema":"public"
        },
        "name":"full_name",
        "cascade": false
    }
}

Args syntax¶

Key	Required	Schema	Description
table	true	TableName	Name of the table
name	true	ComputedFieldName	Name of the computed field
cascade	false	Boolean	When set to `true`, all the dependent items (if any) on this computed fields are also dropped

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