updateMask property

A field mask that specifies the metadata table properties that are overwritten by the update.

Fields specified in the update_mask are relative to the resource (not to the full request). A field is overwritten if it is in the mask.For example, given the target properties: properties { a: 1 b: 2 } And an update properties: properties { a: 2 b: 3 c: 4 } then if the field mask is:paths: "properties.b", "properties.c"then the result will be: properties { a: 1 b: 3 c: 4 }