ReadBulkRelationships API

[mateenkasim]

Problem Statement

I have many situations where I want to read many relationships, but ReadRelationships restricts me to reading them one at a time. Most prohibitively, this happens when I want to read a relationship for every item in a list response.

Consider this schema:

definition folder {}

definition document {
    relation parent: folder
}

Let's say my API wants to send a user a specific list of documents, with the namespace (in this case, just the name of the parent folder) included:

[
    {
        "id": "DocumentA",
        "namespace": "FolderA",
    },
    {
        "id": "DocumentB",
        "namespace": "FolderB",
    },
    {
        "id": "DocumentC",
        "namespace": "FolderC",
    }
]

If I have a length n list of documents alone, such as ["document:DocumentA", "document:DocumentB", "document:DocumentC"], I have to make n SpiceDB ReadRelationships requests to fill out those namespaces. Each request would be of this form:

ReadRelationships(
    ReadRelationshipsRequest(
        consistency=Consistency(...),
        relationship_filter=RelationshipFilter(
            resource_type="document",
            optional_resource_id="DocumentX", # Exact ID specified
            optional_relation="parent",
            optional_subject_filter=SubjectFilter(
                subject_type="folder",
            ),
        ),
    )
)

Once I have the list of parent folders, there does exist a CheckBulkPermissions API, where I can check access to each element in the list using one request, which is great. I would love to read the initial relationships in one request as well.

Solution Brainstorm

A ReadBulkRelationships API akin to the CheckBulkPermissions API would be excellent.

For the example I mentioned above, the desired relationships are somewhat "homogeneous": we're reading the same relation for the same definition type, with only the IDs differing. You can imagine a variant of RelationshipFilter that accepts a list of optional_resource_ids for just this purpose, though I haven't fully thought this interface through. This can definitely be optimized in the SQL to avoid n separate queries. This interface is most useful for me and seems to benefit the most from such an interface.

In general, a user might want "heterogeneous" calls: a list of completely disparate RelationshipFilters to be returned in one response. SpiceDB would return a relationship if it matched any of the given filters. This might not benefit as much at the database query level, but it would certainly benefit from reduced network overhead. I would utilize this in performance-sensitive areas of my app.

Thanks for your time!