active_model_serializers（包括），以及为什么序列化程序正在查询数据？

Question

When working with API, I am used to:

1. execute some DB queries
2. select the data I want in my response
3. serialize the data, and send it to the client

Now , using active_model_serializers , I was assuming that in

render json: artist, include: 'tracks'

the include: 'tracks' part would serialize tracks , if my artist had some tracks.

But apparently, it will also fetch the tracks from the db for me.

Is it a normal behaviour ? Is the serializer supposed to make db queries ?

Answer 1

Yes, to include a association it first has to be fetched from the database. Otherwise how can it be included in the response?

See the json serializer documentation .

The association is called by it's corresponding method. In your example that would be Artist#tracks . (See the source code .) This means that if you load the association before calling the serializer it will not call the database.

Example:

artist = Artist.first # <= artists table gets queried
artist.tracks.load # <= tracks table gets queried
render json: artist, include: :tracks # <= no queries