From bfed0407ca3a59209624185a0c2e27ec5446d01a Mon Sep 17 00:00:00 2001
From: Ludwig Stockbauer-Muhr <35834861+stockbal@users.noreply.github.com>
Date: Wed, 16 Oct 2024 11:49:49 +0200
Subject: [PATCH] feat: add static property `elements` to entity classes (#345)

---
 CHANGELOG.md                       |  1 +
 lib/components/basedefs.js         |  4 ++++
 lib/components/wrappers.js         |  8 ++++++++
 lib/visitor.js                     | 11 ++++++++++-
 test/unit/files/elements/model.cds | 19 +++++++++++++++++++
 test/unit/files/elements/model.ts  | 26 ++++++++++++++++++++++++++
 6 files changed, 68 insertions(+), 1 deletion(-)
 create mode 100644 test/unit/files/elements/model.cds
 create mode 100644 test/unit/files/elements/model.ts

diff --git a/CHANGELOG.md b/CHANGELOG.md
index be0fce05..a17eb11d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
 ## Version 0.28.0 - TBD
 ### Added
 - Schema definition for `cds.typer` options in `package.json` and `.cdsrc-*.json` files
+- Added a static `elements` property to all entities, which allows access to the `LinkedDefinitions` instance of an entity's elements
 - Schema definition for `typescript` cds build task.
 
 ### Fixed
diff --git a/lib/components/basedefs.js b/lib/components/basedefs.js
index 763fcf3b..482baa72 100644
--- a/lib/components/basedefs.js
+++ b/lib/components/basedefs.js
@@ -13,6 +13,10 @@ const timeRegex = '`${number}${number}:${number}${number}:${number}${number}`'
 const baseDefinitions = new SourceFile('_')
 // FIXME: this should be a library someday
 baseDefinitions.addPreamble(`
+import { type } from '@sap/cds'
+
+export type ElementsOf<T> = {[name in keyof Required<T>]: type }
+
 export namespace Association {
     export type to <T> = T;
     export namespace to {
diff --git a/lib/components/wrappers.js b/lib/components/wrappers.js
index d442e5ed..cd9626db 100644
--- a/lib/components/wrappers.js
+++ b/lib/components/wrappers.js
@@ -17,6 +17,13 @@ const createKey = t => `${base}.Key<${t}>`
  */
 const createKeysOf = t => `${base}.KeysOf<${t}>`
 
+/**
+ * Wraps type into ElementsOf type.
+ * @param {string} t - the type name.
+ * @returns {string}
+ */
+const createElementsOf = t => `${base}.ElementsOf<${t}>`
+
 /**
  * Wraps type into association to scalar.
  * @param {string} t - the singular type name.
@@ -102,6 +109,7 @@ module.exports = {
     createArrayOf,
     createKey,
     createKeysOf,
+    createElementsOf,
     createObjectOf,
     createPromiseOf,
     createUnionOf,
diff --git a/lib/visitor.js b/lib/visitor.js
index fdac4432..53a20b2d 100644
--- a/lib/visitor.js
+++ b/lib/visitor.js
@@ -8,7 +8,7 @@ const { SourceFile, FileRepository, Buffer, Path } = require('./file')
 const { FlatInlineDeclarationResolver, StructuredInlineDeclarationResolver } = require('./components/inline')
 const { Resolver } = require('./resolution/resolver')
 const { LOG } = require('./logging')
-const { docify, createPromiseOf, createUnionOf, createKeysOf } = require('./components/wrappers')
+const { docify, createPromiseOf, createUnionOf, createKeysOf, createElementsOf } = require('./components/wrappers')
 const { csnToEnumPairs, propertyToInlineEnumName, isInlineEnumType, stringifyEnumType } = require('./components/enum')
 const { isReferenceType } = require('./components/reference')
 const { empty } = require('./components/typescript')
@@ -167,6 +167,14 @@ class Visitor {
         buffer.add(`declare static readonly keys: ${createKeysOf(clean)}`)
     }
 
+    /**
+     * @param {Buffer} buffer - the buffer to write the elements into
+     * @param {string} clean - the clean name of the entity
+     */
+    #printStaticElements(buffer, clean) {
+        buffer.add(`declare static readonly elements: ${createElementsOf(clean)}`)
+    }
+
     /**
      * Transforms an entity or CDS aspect into a JS aspect (aka mixin).
      * That is, for an element A we get:
@@ -281,6 +289,7 @@ class Visitor {
                     buffer.add(`static readonly kind: 'entity' | 'type' | 'aspect' = '${entity.kind}';`)
                 }
                 this.#printStaticKeys(buffer, clean)
+                this.#printStaticElements(buffer, clean)
                 this.#printStaticActions(entity, buffer, ancestorInfos, file)
             }, '};') // end of generated class
         }, '}') // end of aspect
diff --git a/test/unit/files/elements/model.cds b/test/unit/files/elements/model.cds
new file mode 100644
index 00000000..f3861866
--- /dev/null
+++ b/test/unit/files/elements/model.cds
@@ -0,0 +1,19 @@
+namespace elements_test;
+
+aspect A1 {
+    A_f1 : String;
+    A_f2 : String;
+}
+
+entity E1 {
+    key ID: Integer;
+    a : String;
+    b : Integer;
+}
+
+entity E2 : A1 {
+    key ID: String;
+    d: Integer;
+}
+
+entity P1 as projection on E2;
\ No newline at end of file
diff --git a/test/unit/files/elements/model.ts b/test/unit/files/elements/model.ts
new file mode 100644
index 00000000..4cbe575d
--- /dev/null
+++ b/test/unit/files/elements/model.ts
@@ -0,0 +1,26 @@
+import cds from '@sap/cds'
+import { E1, E2, P1 } from '#cds-models/elements_test'
+
+E1.elements
+E1.elements.ID
+E1.elements.a
+E1.elements.b
+// @ts-expect-error
+E1.elements.nonExistent
+
+E2.elements
+E2.elements.d    // from entity E1
+E2.elements.A_f1 // from aspect A1
+
+// check projection
+P1.elements
+P1.elements.ID
+P1.elements.d
+P1.elements.A_f1
+P1.elements.A_f2
+
+// check LinkedDefinitions types
+E1.elements.a.type
+E1.elements.a.kind
+E1.elements.a.items
+E1.elements.a instanceof cds.builtin.classes.String
\ No newline at end of file