fix: fix checking presence of type mapping to interface object

v2/pkg/engine/plan/abstract_selection_rewriter_helpers.go

@@ -466,7 +466,23 @@ func (r *fieldSelectionRewriter) fieldTypeNameFromUpstreamSchema(fieldRef int, e
 
 	node, hasNode := r.upstreamDefinition.NodeByName(enclosingTypeName)
 	if !hasNode {
-		return "", false
+		var interfaceObjectName string
+
+		for _, objCfg := range r.dsConfiguration.FederationConfiguration().InterfaceObjects {
+			if slices.Contains(objCfg.ConcreteTypeNames, string(enclosingTypeName)) {
+				interfaceObjectName = objCfg.InterfaceTypeName
+				break
+			}
+		}
+
+		if interfaceObjectName == "" {
+			return "", false
+		}
+
+		node, hasNode = r.upstreamDefinition.NodeByNameStr(interfaceObjectName)
+		if !hasNode {
+			return "", false
+		}
 	}
 
 	fieldTypeNode, ok := r.upstreamDefinition.FieldTypeNode(fieldName, node)

v2/pkg/engine/plan/abstract_selection_rewriter_test.go

@@ -3667,6 +3667,66 @@ func TestInterfaceSelectionRewriter_RewriteOperation(t *testing.T) {
 				}`,
 			shouldRewrite: false,
 		},
+		{
+			name: "field is an interface object with concrete type fragments",
+			definition: `
+				type User implements Account {
+					id: ID!
+					name: String!
+					surname: String!
+				}
+
+				type Admin implements Account {
+					id: ID!
+					name: String!
+					login: String!
+				}
+
+				interface Account {
+					id: ID!
+					title: String!
+				}
+
+				type Query {
+					user: Account!
+				}`,
+			upstreamDefinition: `
+				type Account @key(fields: "id") @interfaceObject {
+					id: ID!
+					title: String!
+				}`,
+			dsConfiguration: dsb().
+				RootNode("Account", "id", "title").
+				WithMetadata(func(m *FederationMetaData) {
+					m.InterfaceObjects = []EntityInterfaceConfiguration{
+						{
+							InterfaceTypeName: "Account",
+							ConcreteTypeNames: []string{"Admin", "User"},
+						},
+					}
+				}).
+				DS(),
+			fieldName: "name",
+			operation: `
+				query {
+					__typename
+					user {
+						... on User {
+							name
+						}
+					}
+				}`,
+			expectedOperation: `
+				query {
+					__typename
+					user {
+						... on User {
+							name
+						}
+					}
+				}`,
+			shouldRewrite: false,
+		},
 	}
 
 	for _, testCase := range testCases {