FieldMask represents a set of symbolic field paths, for example:
paths: "f.a"
paths: "f.b.d"
Here f represents a field in some root message, a and b
fields in the message found in f, and d a field found in the
message in f.b.
Field masks are used to specify a subset of fields that should be
returned by a get operation or modified by an update operation.
Field masks also have a custom JSON encoding (see below).
Field Masks in Projections
When used in the context of a projection, a response message or
sub-message is filtered by the API to only contain those fields as
specified in the mask. For example, if the mask in the previous
example is applied to a response message as follows:
f {
a : 22
b {
d : 1
x : 2
}
y : 13
}
z: 8
The result will not contain specific values for fields x,y and z
(their value will be set to the default, and omitted in proto text
output):
f {
a : 22
b {
d : 1
}
}
A repeated field is not allowed except at the last position of a
paths string.
If a FieldMask object is not present in a get operation, the
operation applies to all fields (as if a FieldMask of all fields
had been specified).
Note that a field mask does not necessarily apply to the
top-level response message. In case of a REST get operation, the
field mask applies directly to the response, but in case of a REST
list operation, the mask instead applies to each individual message
in the returned resource list. In case of a REST custom method,
other definitions may be used. Where the mask applies will be
clearly documented together with its declaration in the API. In
any case, the effect on the returned resource/resources is required
behavior for APIs.
Field Masks in Update Operations
A field mask in update operations specifies which fields of the
targeted resource are going to be updated. The API is required
to only change the values of the fields as specified in the mask
and leave the others untouched. If a resource is passed in to
describe the updated values, the API ignores the values of all
fields not covered by the mask.
If a repeated field is specified for an update operation, new values will
be appended to the existing repeated field in the target resource. Note that
a repeated field is only allowed in the last position of a paths string.
If a sub-message is specified in the last position of the field mask for an
update operation, then new value will be merged into the existing sub-message
in the target resource.
For example, given the target message:
f {
b {
d: 1
x: 2
}
c: [1]
}
And an update message:
f {
b {
d: 10
}
c: [2]
}
then if the field mask is:
paths: ["f.b", "f.c"]
then the result will be:
f {
b {
d: 10
x: 2
}
c: [1, 2]
}
An implementation may provide options to override this default behavior for
repeated and message fields.
In order to reset a field's value to the default, the field must
be in the mask and set to the default value in the provided resource.
Hence, in order to reset all fields of a resource, provide a default
instance of the resource and set all fields in the mask, or do
not provide a mask as described below.
If a field mask is not present on update, the operation applies to
all fields (as if a field mask of all fields has been specified).
Note that in the presence of schema evolution, this may mean that
fields the client does not know and has therefore not filled into
the request will be reset to their default. If this is unwanted
behavior, a specific service may require a client to always specify
a field mask, producing an error if not.
As with get operations, the location of the resource which
describes the updated values in the request message depends on the
operation kind. In any case, the effect of the field mask is
required to be honored by the API.
Considerations for HTTP REST
The HTTP kind of an update operation which uses a field mask must
be set to PATCH instead of PUT in order to satisfy HTTP semantics
(PUT must only be used for full updates).
JSON Encoding of Field Masks
In JSON, a field mask is encoded as a single string where paths are
separated by a comma. Fields name in each path are converted
to/from lower-camel naming conventions.
As an example, consider the following message declarations:
message Profile {
User user = 1;
Photo photo = 2;
}
message User {
string display_name = 1;
string address = 2;
}
In proto a field mask for Profile may look as such:
mask {
paths: "user.display_name"
paths: "photo"
}
In JSON, the same mask is represented as below:
{
mask: "user.displayName,photo"
}
Field Masks and Oneof Fields
Field masks treat fields in oneofs just as regular fields. Consider the
following message:
message SampleMessage {
oneof test_oneof {
string name = 4;
SubMessage sub_message = 9;
}
}
The field mask can be:
mask {
paths: "name"
}
Or:
mask {
paths: "sub_message"
}
Note that oneof type names ("test_oneof" in this case) cannot be used in
paths.
Field Mask Verification
The implementation of any API method which has a FieldMask type field in the
request should verify the included field paths, and return an
INVALID_ARGUMENT error if any path is unmappable.
Protobuf type google.protobuf.FieldMask
A method that implements different types of operations described in MethodToInvoke.
These different kinds of operations are required to implement message-level operations for
builders in the runtime. This method bundles those operations to reduce the generated methods
count.
NEW_INSTANCE returns a new instance of the protocol buffer that has not yet been
made immutable. See MAKE_IMMUTABLE.
IS_INITIALIZED returns null for false and the default instance for true.
It doesn't use or modify any memoized value.
GET_MEMOIZED_IS_INITIALIZED returns the memoized isInitialized byte
value.
SET_MEMOIZED_IS_INITIALIZED sets the memoized isInitialized byte value to
1 if the first parameter is not null, or to 0 if the first parameter is null.
NEW_BUILDER returns a BuilderType instance.
This method, plus the implementation of the Builder, enables the Builder class to be proguarded
away entirely on Android.
For use by generated code only.
