By default, Payload's APIs will return all fields for a given collection or global. But, you may not need all of that data for all of your queries. Sometimes, you might want just a few fields from the response.
With the Select API, you can define exactly which fields you'd like to retrieve. This can impact the performance of your queries by affecting the load on the database and the size of the response.
To specify select in the Local API, you can use the select option in your query:
To specify select in the REST API, you can use the select parameter in your query:
To understand the syntax, you need to understand that complex URL search strings are parsed into a JSON object. This one isn't too bad, but more complex queries get unavoidably more difficult to write.
For this reason, we recommend to use the extremely helpful and ubiquitous qs-esm package to parse your JSON / object-formatted queries into query strings:
The defaultPopulate property allows you specify which fields to select when populating the collection from another document. This is especially useful for links where only the slug is needed instead of the entire document.
With this feature, you can dramatically reduce the amount of JSON that is populated from Relationship or Upload fields.
For example, in your content model, you might have a Link field which links out to a different page. When you go to retrieve these links, you really only need the slug of the page.
Loading all of the page content, its related links, and everything else is going to be overkill and will bog down your Payload APIs. Instead, you can define the defaultPopulate property on your Pages collection, so that when Payload "populates" a related Page, it only selects the slug field and therefore returns significantly less JSON:
Setting defaultPopulate will enforce that each time Payload performs a "population" of a related document, only the fields specified will be queried and returned. However, you can override defaultPopulate with the populate property in the Local and REST API:
Local API:
REST API: