Relational Metadata

The rel metadata type provides a syntax for defining relationships between types.

primaryKey

Use primaryKey to indicate that a property or parameter refers to the primary key of an object.

Applied to:

• Property
• Parameter

Schema:

• primaryKey [true] - Value (always true) that indicates that the parent property or parameter refers to an object's primary key.

Example:

{ "primaryKey": true }

Property

Add a primary key to a property to indicate that the property is this type's primary key.

Example in context (JSONSchema/OpenAPI):

{
  "type": "object",
  "properties": {
    "id": {
      "type": "string",
      "x-rel": { "primaryKey": true } // Indicates that "id" is this object's primary key
    },
    "name": { "type": "string" },
    "value": { "type": "number" }
  }
}

Parameter

Add a primary key to a method parameter to indicate that the supplied argument is the primary key of the root type returned by the method.

If the method return type is an object or array, then the root type the object's type of the type of the array element. If the method type is an "envelop" (an object with an errors array and a wrapped data, value, or values property), then the root type referres to the type of the wrapped property.

Example in context (OpenAPI):

{
  "operationId": "getGizmos",
  "parameters": [
    {
      "name": "widgetId",
      "in": "query",
      "type": "string",
      "x-rel": { "primaryKey": true } // Indicates that "widgetId" refers to the "id" property on the return value's root type
    }
  ]
}

foreignKey

Add foreignKey to indicate a foreign key relationship to a type's primary key.

Applied to:

• Property
• Parameter

Schema:

• foreignKey/type [String] - Name of the foreign type. (Note that the type does not need to be defined locally.)
• foreignKey/property [String] - Name of the primary key property on the foreign type.
• foreignKey/many [Boolean (optional)] - When true, indicates that there may be many of the parent type associated to one of the foreign type. If false or not supplied, then it is understood that there is a one-to-one relationship between the two types.

Example:

{
  "foreignKey": {
    "type": "user",
    "property": "id",
    "many": true
  }
}

Property

Add a foreign key to a property to indicate that the value of that property is the primary key of another type.

Example in context (JSONSchema/OpenAPI):

{
  "type": "object",
  "properties": {
    "id": { "type": "string" },
    "widgetId": {
      "type": "string",
      "x-rel": {
        "foreignKey": {
          // Indicates that "widgetId" refers to the "id" property on the type "widget"
          "type": "widget",
          "property": "id",
          "many": true
        }
      }
    },
    "value": { "type": "number" }
  }
}

Parameter

Add a foreign key to a method parameter to indicate that the supplied argument(s) are the primary key of a particular type. The many property has no effect when applied to parameters.

Example in context (OpenAPI):

{
  "operationId": "getGizmos",
  "parameters": [
    {
      "name": "widgetId",
      "in": "query",
      "type": "string",
      "x-rel": {
        "foreignKey": {
          // Indicates that "widgetId" refers to the "id" property on the type "widget"
          "type": "widget",
          "property": "id"
        }
      }
    }
  ]
}

When used on a parameter, it is assumed that the foreign key will be represented on the method return value root type as type + property. (Eg. for type widget and property id, then the return value root type is expecte to have a method called widgetId.) If the property on the root type is named something different, then the property name can be specified with a localProperty value:

{
  "foreignKey": {
    "type": "widget",
    "property": "id",
    "localProperty": "defaultWidgetId"
  }
}

Note that localProperty only has an effect when applied to Parameters.

edge

Add edge to a type to define a many-to-many edge between to types. For example, to define a many-to-many edge between the product and order types, create a productOrder type with a foreign key to both products and orders. Then, add an edge rel object that includes both foreign key properties. Doing so will establish the many-to-many relationship.

Often, only defining two foreign keys is enough to describe the relationship between types. The "edge" metadata indicates that the decorated type is not a first-class domain object, but rather data that describes the relationship between two other first-class domain objects. If the decorated type is relevant on its own (eg. you don't need to also query for one or both of the related types), then you probably don't need to apply edge metatdata.

Schema:

• edge [Array(String, String)] - A tuple continaing the name of two properties on this type that are foreign keys to the two joined types.

Usage:

{ "edge": ["productId", "orderId"] }

Example in context (JSONSchema/OpenAPI):

{
  "type": "object",
  "x-rel": {
    "edge": ["productId", "orderId"] // Indicates that this type is an "edge" between products and orders
  },
  "properties": {
    "id": { "type": "string" },
    "quantity": { "type": "integer" },
    "productId": {
      "type": "string",
      "x-rel": {
        "foreignKey": {
          // foreign key to product type
          "type": "product",
          "property": "id",
          "many": true
        }
      }
    },
    "orderId": {
      "type": "string",
      "x-rel": {
        "foreignKey": {
          // foreign key to order type
          "type": "order",
          "property": "id",
          "many": true
        }
      }
    }
  }
}

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