poc add ability to use any unique key as the external 'id'

this makes it possible to use a natural key even while also using surrogate primary keys

Author: lsmith77

packages/runtime/src/cross/utils.ts

@@ -50,9 +50,17 @@ export function zip<T1, T2>(x: Enumerable<T1>, y: Enumerable<T2>): Array<[T1, T2
  * Gets ID fields of a model.
  */
 export function getIdFields(modelMeta: ModelMeta, model: string, throwIfNotFound = false) {
-    const uniqueConstraints = modelMeta.models[lowerCaseFirst(model)]?.uniqueConstraints ?? {};
+    const metaData = modelMeta.models[lowerCaseFirst(model)] ?? {};
+    const uniqueConstraints = metaData.uniqueConstraints ?? {};
+
+    let entries = Object.values(uniqueConstraints);
+    if (metaData.attributes !== undefined) {
+        const externalId = metaData.attributes.find((attr) => attr.name === '@@externalId');
+        if (externalId && externalId.args[0] !== undefined) {
+            entries = entries.filter((entry) => entry.name === externalId.args[0].value);
+        }
+    }
 
-    const entries = Object.values(uniqueConstraints);
     if (entries.length === 0) {
         if (throwIfNotFound) {
             throw new Error(`Model ${model} does not have any id field`);

packages/schema/src/res/stdlib.zmodel

@@ -738,6 +738,11 @@ attribute @@prisma.passthrough(_ text: String)
  */
 attribute @@delegate(_ discriminator: FieldReference)
 
+/**
+ * Specifies an external identifier for the model other than a primary key
+ */
+attribute @@externalId(_ name: String)
+
 /**
  * Used for specifying operator classes for GIN index.
  */