I want to serialize relation using Active Model Serializers and I want to set some 'global' attributes (e.g. count) for this relation:
{
users: {
total: 12,
page: 2,
users: [{}, {}, {}, ...]
}
}
How could I do that?
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3 Answers
During your render call in the controller, you can pass in the meta attribute.
render @users, :each_serializer => UserSerializer, :meta => { :total => @users.count }
This will produce the following JSON:
{
"users" : [...],
"meta" : {
"total" : 12
}
}
You can rename the meta key name by passing in the meta_key option.
3 Comments
rmcsharry
This is the correct json structure for JSONAPI specification, so this is what you should return to comply with the spec - a meta attribute
rmcsharry
Note that this does have the same database impact as the answer from @Stanislav if you trigger this code as a result of calling a parent serialiser (you will fire a count query for every parent). On very large datasets (probably millions of rows) this will get slow. Just sayin' :)
rmcsharry
You can define calculated properties in your serializer:
class FooSerializer < ActiveModel::Serializer
attributes :users_count
has_many :users
def users_count
object.users.size
end
end
2 Comments
rmcsharry
This works and is ok for small datasets. Just be aware that this will fire a user count query for every Foo. So when hitting foo/index route, if you return 100 foo's: one query to get the Foos followed by 100 "select count(*) from users where foo.id=x"
rmcsharry
This will not make multiple DB calls for count as pointed out by
@rmcsharry
{
data: ActiveModelSerializers::SerializableResource.new(
@users, each_serializer: UserSerializer).as_json,
count: @users.count
}
answered Aug 28, 2020 at 9:38
Indrajith Indraprastham
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