pub enum Predicate {
FirstOrder(FirstOrder),
SecondOrder(SecondOrder),
}Expand description
A Predicate is an Object whose members describe a testable condition that evaluates as either true or false.
The essential components of a Predicate include:
- A label identifying the predicate operation,
- A reference to the value being tested, and
- The condition against which the referenced value is to be evaluated.
Predicate objects MUST have exactly one “op” member whose value indicates the type of predicate operation to perform. It’s value MUST be one of: “and”, “contains”, “contains-”, “defined”, “ends”, “ends-”, “in”, “in-”, “less”, “matches”, “matches-”, “more”, “not”, “or”, “starts”, “starts-”, “test”, “test-”, “type”, or “undefined”.
The semantics for each are defined in the sections that follow.
Note that the value of the “op” member is case-sensitive and that each of the operations listed are in lower-case. The value “Starts”, for example, is not equivalent to “starts”.
If the “op” member specifies any value other than one of those listed above, the evaluation of the predicate operation MUST cease and be handled as if a boolean value of “false” was returned. The application processing the predicate operation MAY signal that an error condition has occurred depending on the specific requirements of the application within which JSON Predicates are being used.
The remaining structure of each predicate operation depends on the specific type. There are two basic types of predicates.
-
First Order Predicates that are used to test one name value pair against a single condition, and
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Second Order Predicates that aggregate one or more subordinate First or Second Order Predicates.
In addition to the required “op” member, First Order Predicates have exactly one “path” member whose value MUST be a string containing a JSON-Pointer RFC6901 value referencing the name value pair that is to be tested. If the “path” member is not specified within the predicate object, it’s value is assumed to be an empty string.
Second Order Predicates MUST have exactly one “apply” member whose value is a JSON Array containing one or more First or Second Order Predicate Objects.
Additional members can be required depending on the specific predicate operation. All other members not explicitly defined by this specification MUST be ignored.
Note that the ordering of members in JSON objects is not significant; therefore the following operations are equivalent:
{"op": "contains", "path": "/a/b/c", "value": "ABC"}
{"path": "/a/b/c", "op": "contains", "value": "ABC"}
{"value": "ABC", "path": "/a/b/c", "op": "contains"}