Variables

A QueryRequest can optionally specify one or more sets of variables which can be referenced throughout the Query object.

Query variables will only be provided if the query.variables capability is advertised in the capabilities response.

The intent is that the data connector should attempt to perform multiple versions of the query in parallel - one instance of the query for each set of variables. For each set of variables, each variable value should be substituted wherever it is referenced in the query - for example in a ComparisonValue.

Example

In the following query, we fetch two rowsets of article data. In each rowset, the rows are filtered based on the author_id column, and the prescribed author_id is determined by a variable. The choice of author_id varies between rowsets.

The result contains one rowset containing articles from the author with ID 1, and a second for the author with ID 2.

{
    "collection": "articles",
    "arguments": {},
    "query": {
        "fields": {
            "id": {
                "type": "column",
                "column": "id"
            },
            "title": {
                "type": "column",
                "column": "title"
            }
        },
        "predicate": {
            "type": "binary_comparison_operator",
            "column": {
                "type": "column",
                "name": "id",
                "path": []
            },
            "operator": "eq",
            "value": {
                "type": "variable",
                "name": "$article_id"
            }
        }
    },
    "collection_relationships": {},
    "variables": [
        {
            "$article_id": 1
        },
        {
            "$article_id": 2
        }
    ]
}

Requirements

• If variables are provided in the QueryRequest, then the QueryResponse should contain one RowSet for each set of variables.
• If variables are not provided, the data connector should return a single RowSet.