Support filtering relationships by _id

packages/server/src/api/routes/tests/search.spec.ts

@@ -3553,6 +3553,28 @@ if (descriptions.length) {
                     limit: 1,
                   }).toContainExactly([row])
                 })
+
+                it("can filter by the related _id", async () => {
+                  await expectSearch({
+                    query: {
+                      equal: { "rel._id": row.rel[0]._id },
+                    },
+                  }).toContainExactly([row])
+
+                  await expectSearch({
+                    query: {
+                      equal: { "rel._id": row.rel[1]._id },
+                    },
+                  }).toContainExactly([row])
+                })
+
+                it("can filter by the related _id and find nothing", async () => {
+                  await expectSearch({
+                    query: {
+                      equal: { "rel._id": "rel_none" },
+                    },
+                  }).toFindNothing()
+                })
               })
 
             !isInternal &&

packages/server/src/sdk/app/rows/queryUtils.ts

@@ -69,7 +69,8 @@ export const getQueryableFields = async (
     fromTables: string[],
     opts?: { noRelationships?: boolean }
   ): Promise<string[]> => {
-    const result = []
+    // Querying by _id is always allowed, even if it's never part of the schema
+    const result = ["_id"]
     for (const field of Object.keys(table.schema).filter(
       f => allowedFields.includes(f) && table.schema[f].visible !== false
     )) {
@@ -113,9 +114,7 @@ export const getQueryableFields = async (
     return result
   }
 
-  const result = [
-    "_id", // Querying by _id is always allowed, even if it's never part of the schema
-  ]
+  const result = []
 
   if (fields == null) {
     fields = Object.keys(table.schema)