Allow query_cluster: null in datastore config to hide types

elasticgraph-datastore_core/lib/elastic_graph/datastore_core/config.rb

@@ -132,9 +132,9 @@ class Config < Support::Config.define(:client_faraday_adapter, :clusters, :index
                 }],
                 properties: {
                   query_cluster: {
-                    type: "string",
-                    description: "Named search cluster to be used for queries on this index. The value must match be a key in the `clusters` map.",
-                    examples: ["main", "search_cluster"]
+                    type: ["string", "null"],
+                    description: "Named search cluster to be used for queries on this index. The value must match be a key in the `clusters` map. Set to `null` to hide this index's types in the GraphQL schema returned from the GraphQL endpoint.",
+                    examples: ["main", "search_cluster", nil]
                   },
                   index_into_clusters: {
                     type: "array",

elasticgraph-datastore_core/sig/elastic_graph/datastore_core/configuration/index_definition.rbs

@@ -3,15 +3,15 @@ module ElasticGraph
     module Configuration
       class IndexDefinitionSupertype
         attr_reader ignore_routing_values: ::Set[::String]
-        attr_reader query_cluster: ::String
+        attr_reader query_cluster: ::String?
         attr_reader index_into_clusters: ::Array[::String]
         attr_reader setting_overrides: ::Hash[::String, untyped]
         attr_reader setting_overrides_by_timestamp: ::Hash[::String, ::Hash[::String, untyped]]
         attr_reader custom_timestamp_ranges: ::Array[IndexDefinition::CustomTimestampRange]
 
         def initialize: (
           ignore_routing_values: ::Set[::String],
-          query_cluster: ::String,
+          query_cluster: ::String?,
           index_into_clusters: ::Array[::String],
           setting_overrides: ::Hash[::String, untyped],
           setting_overrides_by_timestamp: ::Hash[::String, ::Hash[::String, untyped]],
@@ -20,7 +20,7 @@ module ElasticGraph
 
         def with: (
           ?ignore_routing_values: ::Set[::String],
-          ?query_cluster: ::String,
+          ?query_cluster: ::String?,
           ?index_into_clusters: ::Array[::String],
           ?setting_overrides: ::Hash[::String, untyped],
           ?setting_overrides_by_timestamp: ::Hash[::String, ::Hash[::String, untyped]],

elasticgraph-datastore_core/spec/unit/elastic_graph/datastore_core/config_spec.rb

@@ -97,6 +97,43 @@ class DatastoreCore
         expect(config.max_client_retries).to eq 3
       end
 
+      it "allows `query_cluster: null` to hide index types from GraphQL schema" do
+        config = config_from_yaml(<<~YAML)
+          client_faraday_adapter: {}
+          clusters:
+            main1:
+              url: http://example.com/1234
+              backend: elasticsearch
+              settings:
+                foo: 23
+          index_definitions:
+            widgets:
+              query_cluster: null
+              index_into_clusters: ["main1"]
+              ignore_routing_values: []
+              setting_overrides: {}
+              setting_overrides_by_timestamp: {}
+              custom_timestamp_ranges: []
+        YAML
+
+        widgets_config = config.index_definitions.fetch("widgets")
+
+        # Verify the config was loaded correctly from YAML
+        expect(widgets_config).to eq(Configuration::IndexDefinition.new(
+          ignore_routing_values: [],
+          query_cluster: nil,
+          index_into_clusters: ["main1"],
+          setting_overrides: {},
+          setting_overrides_by_timestamp: {},
+          custom_timestamp_ranges: []
+        ))
+
+        # Verify the key property: query_cluster is nil (not a string, not missing)
+        # This nil value will cause accessible_from_queries? to return false,
+        # which hides the index's types from the GraphQL schema.
+        expect(widgets_config.query_cluster).to be_nil
+      end
+
       it "surfaces misspellings in `backend`" do
         expect {
           config_from_yaml(<<~YAML)

elasticgraph-local/lib/elastic_graph/local/spec_support/config_schema.yaml

@@ -141,12 +141,17 @@ properties:
                   number_of_shards: 32
             properties:
               query_cluster:
-                type: string
+                type:
+                - string
+                - 'null'
                 description: Named search cluster to be used for queries on this index.
-                  The value must match be a key in the `clusters` map.
+                  The value must match be a key in the `clusters` map. Set to `null`
+                  to hide this index's types in the GraphQL schema returned from the
+                  GraphQL endpoint.
                 examples:
                 - main
                 - search_cluster
+                -
               index_into_clusters:
                 type: array
                 items: