Field masks are a way for API callers to list the fields that a request should return or update. Using a FieldMask allows the API to avoid unnecessary work and improves performance. A field mask is used for both the read and update methods in the Google Slides API.
Read with a field mask
Presentations can be large, and often you don't need every part of the
Presentation
resource returned by a read request. You can limit what's returned in a
Slides API response, using the fields
URL parameter. For best
performance,
explicitly list only the fields you need
in the reply.
The format of the fields parameter is the same as the JSON encoding of a FieldMask. Stated briefly, multiple different fields are comma-separated and subfields are dot-separated. Field names can be specified in camelCase or separated_by_underscores. For convenience, multiple subfields from the same type can be listed within parentheses.
The following presentations.get
request example uses a field mask of
slides.pageElements(objectId,size,transform)
to fetch only the object ID,
Size
, and
transform
of a pageElement
object on all slides in a presentation:
GET https://slides.googleapis.com/v1/presentations/presentationId?fields=slides.pageElements(objectId,size,transform)
The response to this method call is a
Presentation
object
containing the components requested in the field mask:
{ "slides": [ { "pageElements": [ { "objectId": "OBJECT_ID
", "size": { "width": { "magnitude": 3000000, "unit": "EMU" }, "height": { "magnitude": 3000000, "unit": "EMU" } }, "transform": { "scaleX": 1, "scaleY": 1 "translateX": 311708, "translateY": 744575, "unit": "EMU" } }, { "objectId": "OBJECT_ID
", "size": { "width": { "magnitude": 3000000, "unit": "EMU" }, "height": { "magnitude": 3000000, "unit": "EMU" } }, "transform": { "scaleX": 1, "scaleY": 1 "translateX": 311700, "translateY": 2834125, "unit": "EMU" } } ] } ] }
Update with a field mask
Sometimes you need to update only certain fields in an object while leaving the
other fields unchanged. Update requests inside a
presentations.batchUpdate
operation use field masks to tell the API which fields are being changed. The
update request ignores any fields that aren't specified in the field mask,
leaving them with their current values.
You can also unset a field by not specifying it in the updated message, but adding the field to the mask. This clears whatever value the field previously had.
The syntax for update field masks is the same as read field masks.
The following example uses the
UpdateShapePropertiesRequest
to change a shape's color fill to the DARK1
theme color and unset the shape's
outline:
POST https://slides.googleapis.com/v1/presentations/presentationId:batchUpdate
{
"requests": [
{
"updateShapeProperties": {
"objectId": OBJECT_ID
,
"shapeProperties": {
"shapeBackgroundFill": {
"solidFill": {
"color": {
"themeColor": "DARK1"
}
}
}
},
"fields": "shapeBackgroundFill.solidFill.color,outline"
}
}
]
}