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4. Operations

Operation objects MUST have exactly one "op" member, whose value indicates the operation to perform. Its value MUST be one of "add", "remove", "replace", "move", "copy", or "test"; other values are errors. The semantics of each object is defined below.

Additionally, operation objects MUST have exactly one "path" member. That member's value is a string containing a JSON-Pointer value [RFC6901] that references a location within the target document (the "target location") where the operation is performed.

The meanings of other operation object members are defined by operation (see the subsections below). Members that are not explicitly defined for the operation in question MUST be ignored (i.e., the operation will complete as if the undefined member did not appear in the object).

Note that the ordering of members in JSON objects is not significant; therefore, the following operation objects are equivalent:

{ "op": "add", "path": "/a/b/c", "value": "foo" }
{ "path": "/a/b/c", "op": "add", "value": "foo" }
{ "value": "foo", "path": "/a/b/c", "op": "add" }

Operations are applied to the data structures represented by a JSON document, i.e., after any unescaping (see [RFC4627], Section 2.5) takes place.

4.1. add​

The "add" operation performs one of the following functions, depending upon what the target location references:

  • If the target location specifies an array index, a new value is inserted into the array at the specified index.

  • If the target location specifies an object member that does not already exist, a new member is added to the object.

  • If the target location specifies an object member that does exist, that member's value is replaced.

The operation object MUST contain a "value" member whose content specifies the value to be added.

For example:

{ "op": "add", "path": "/a/b/c", "value": [ "foo", "bar" ] }

When the operation is applied, the target location MUST reference one of:

  • The root of the target document - whereupon the specified value becomes the entire content of the target document.

  • A member to add to an existing object - whereupon the supplied value is added to that object at the indicated location. If the member already exists, it is replaced by the specified value.

  • An element to add to an existing array - whereupon the supplied value is added to the array at the indicated location. Any elements at or above the specified index are shifted one position to the right. The specified index MUST NOT be greater than the number of elements in the array. If the "-" character is used to index the end of the array (see [RFC6901]), this has the effect of appending the value to the array.

Because this operation is designed to add to existing objects and arrays, its target location will often not exist. Although the pointer's error handling algorithm will thus be invoked, this specification defines the error handling behavior for "add" pointers to ignore that error and add the value as specified.

However, the object itself or an array containing it does need to exist, and it remains an error for that not to be the case. For example, an "add" with a target location of "/a/b" starting with this document:

{ "a": { "foo": 1 } }

is not an error, because "a" exists, and "b" will be added to its value. It is an error in this document:

{ "q": { "bar": 2 } }

because "a" does not exist.

4.2. remove​

The "remove" operation removes the value at the target location.

The target location MUST exist for the operation to be successful.

For example:

{ "op": "remove", "path": "/a/b/c" }

If removing an element from an array, any elements above the specified index are shifted one position to the left.

4.3. replace​

The "replace" operation replaces the value at the target location with a new value. The operation object MUST contain a "value" member whose content specifies the replacement value.

The target location MUST exist for the operation to be successful.

For example:

{ "op": "replace", "path": "/a/b/c", "value": 42 }

This operation is functionally identical to a "remove" operation for a value, followed immediately by an "add" operation at the same location with the replacement value.

4.4. move​

The "move" operation removes the value at a specified location and adds it to the target location.

The operation object MUST contain a "from" member, which is a string containing a JSON Pointer value that references the location in the target document to move the value from.

The "from" location MUST exist for the operation to be successful.

For example:

{ "op": "move", "from": "/a/b/c", "path": "/a/b/d" }

This operation is functionally identical to a "remove" operation on the "from" location, followed immediately by an "add" operation at the target location with the value that was just removed.

The "from" location MUST NOT be a proper prefix of the "path" location; i.e., a location cannot be moved into one of its children.

4.5. copy​

The "copy" operation copies the value at a specified location to the target location.

The operation object MUST contain a "from" member, which is a string containing a JSON Pointer value that references the location in the target document to copy the value from.

The "from" location MUST exist for the operation to be successful.

For example:

{ "op": "copy", "from": "/a/b/c", "path": "/a/b/e" }

This operation is functionally identical to an "add" operation at the target location using the value specified in the "from" member.

4.6. test​

The "test" operation tests that a value at the target location is equal to a specified value.

The operation object MUST contain a "value" member that conveys the value to be compared to the target location's value.

The target location MUST be equal to the "value" value for the operation to be considered successful.

Here, "equal" means that the value at the target location and the value conveyed by "value" are of the same JSON type, and that they are considered equal by the following rules for that type:

  • strings: are considered equal if they contain the same number of Unicode characters and their code points are byte-by-byte equal.

  • numbers: are considered equal if their values are numerically equal.

  • arrays: are considered equal if they contain the same number of values, and if each value can be considered equal to the value at the corresponding position in the other array, using this list of type-specific rules.

  • objects: are considered equal if they contain the same number of members, and if each member can be considered equal to a member in the other object, by comparing their keys (as strings) and their values (using this list of type-specific rules).

  • literals (false, true, and null): are considered equal if they are the same.

Note that the comparison that is done is a logical comparison; e.g., whitespace between the member values of an array is not significant.

Also, note that ordering of the serialization of object members is not significant.

For example:

{ "op": "test", "path": "/a/b/c", "value": "foo" }