Class FieldMask

java.lang.Object
com.google.protobuf.AbstractMessageLite
com.google.protobuf.AbstractMessage
com.google.protobuf.GeneratedMessage
com.google.protobuf.FieldMask
All Implemented Interfaces:
FieldMaskOrBuilder, Message, MessageLite, MessageLiteOrBuilder, MessageOrBuilder, Serializable
@Generated public final class FieldMask extends GeneratedMessage implements FieldMaskOrBuilder
`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.

Note that libraries which implement FieldMask resolution have various
different behaviors in the face of empty masks or the special "*" mask.
When implementing a service you should confirm these cases have the
appropriate behavior in the underlying FieldMask library that you desire,
and you may need to special case those cases in your application code if
the underlying field mask library behavior differs from your intended
service semantics.

Update methods implementing https://google.aip.dev/134
- MUST support the special value * meaning "full replace"
- MUST treat an omitted field mask as "replace fields which are present".

Other methods implementing https://google.aip.dev/157
- SHOULD support the special value "*" to mean "get all".
- MUST treat an omitted field mask to mean "get all", unless otherwise
documented.

## 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
See Also: