Support using query string parameters on JSON-mapped columns

[bkoelman]

Entity Framework Core 8 adds improved support for filtering, sorting, and projecting JSON-mapped columns. And PostgreSQL support has been implemented since v8.

This issue tracks the work for implementing similar support for JSON:API. It would potentially enable filters such as /users?filter(equals(address.country,'Netherlands')) where Address is stored as a keyless JSON object in the Users table.

[bkoelman]

After some experimentation, it turns out that this requires major breaking changes throughout the types used in the resource graph, query expression types, query string parsing, the translation to System.Expression and parsing request bodies. The fundamental change is that now both a ResourceType and an AttrAttribute can have child attributes, so I introduced a common interface. Consequently, every place that uses ResourceType now also needs to account for the compound-attribute case.

Basically, the support for Keyless entities in EF Core 8/9 is pretty limited, not yet supporting key use cases such as collections. This is clearly still a work-in-progress. So I switched to the older Owned entities, which works well for simple cases (although the database mapping quickly becomes complex or even impossible).

I suspect the feature can be built today using Owned entities, so that users can switch to Keyless entities once it has matured, without requiring changes to JsonApiDotNetCore. However, this is still a lot of work!

Update: According to here, Keyless entities should be fully functional in EF Core 10.

[bkoelman]

I wondered whether a PATCH resource request should be able to update a subset of fields in the JSON value. Based on this and the fact that there's no JSON:API syntax to express collection changes (which is what JSON-Patch provides), I've arrived at the conclusion that a patch request should always be a full replacement.