Select | @m-ld/m-ld

A query pattern that returns values for variables in the query.

The subjects streamed in the query result will have the form:

{
  "?var1": <value>
  "?var2": <value>
  ...
}

Examples:

Select the ids of subjects having a given name

{
  "@select": "?id",
  "@where": {
    "@id": "?id",
    "name": "Wilma"
  }
}

Select the ids and names of all subjects

{
  "@select": ["?id", "?value"],
  "@where": {
    "@id": "?id",
    "name": "?value"
  }
}

See the @where property for more examples of how to use a where clause.

see: json-rql select

Hierarchy

Read
- Select

Index

Properties

Optional @context

@context: Context

An optional JSON-LD Context for the query. Use of a query-specific Context is rarely required, as the context is typically the local application, whose needs are specified by the local clone configuration.

@select

@select: Result

A declaration of the selection of variables that will be returned.

Optional @where

@where: Subject | Subject[] | Group

The data pattern to match, as a set of subjects or a group. Variables are used as placeholders to capture matching properties and values in the domain.

Examples:

Match a subject by its @id

{
  ...
  "@where": { "@id": "fred" }
}

Match a subject where any property has a given value

{
  ...
  "@where": {
    "@id": "?id",
    "?prop": "Bedrock"
  }
}

Match a subject with a given property, having any value

{
  ...
  "@where": {
    "@id": "?id",
    "name": "?name"
  }
}

The Javascript engine supports exact-matches for subject identities, properties and values. Inline filters will be available in future.

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