From bd5a57189d0f09472d011ba96c5d74d66418852b Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Wed, 16 Jul 2025 13:23:35 +0200
Subject: [PATCH 01/11] feat: PoC for dynamic constraints using standard cds
 views

---
 bookshop/server.js               | 26 +++++++++++++++++
 bookshop/srv/x-field-control.cds | 10 +++++++
 bookshop/srv/x-validation.cds    | 50 ++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+)
 create mode 100644 bookshop/server.js
 create mode 100644 bookshop/srv/x-field-control.cds
 create mode 100644 bookshop/srv/x-validation.cds

diff --git a/bookshop/server.js b/bookshop/server.js
new file mode 100644
index 00000000..46467b15
--- /dev/null
+++ b/bookshop/server.js
@@ -0,0 +1,26 @@
+//
+//  Quick and dirty implementation for cds.validate() using db-level constraints
+//
+
+const cds = require('@sap/cds')
+cds.on('served', ()=> {
+
+  const $ = cds.validate; cds.validate = async function (entity, key, ...columns) {
+    if (!entity.is_entity) return $(...arguments)
+    if (entity.constraints) entity = entity.constraints
+    if (key?.results) key = key.results[0].lastInsertRowid
+    const checks = await SELECT.one.from (entity, key, columns.length && columns)
+    const failed = {}; for (let c in checks) {
+      if (c in entity.keys) continue
+      if (c[0] == '_') continue
+      if (checks[c]) failed[c] = checks[c]
+    }
+    if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
+  }
+
+})
+
+Object.defineProperties (cds.entity.prototype, {
+  constraints: { get() { return cds.model.definitions[this.name+'.constraints'] }},
+  fields: { get() { return cds.model.definitions[this.name+'.field.control'] }},
+})
diff --git a/bookshop/srv/x-field-control.cds b/bookshop/srv/x-field-control.cds
new file mode 100644
index 00000000..9f96d3ad
--- /dev/null
+++ b/bookshop/srv/x-field-control.cds
@@ -0,0 +1,10 @@
+namespace sap.capire.bookshop;
+using from '../db/schema';
+
+view Books.field.control as select from Books { ID,
+  genre.name == 'Drama' ? 'readonly' :
+  null as price
+}
+extend Books with {
+  fc : Association to Books.field.control on fc.ID = $self.ID
+}
diff --git a/bookshop/srv/x-validation.cds b/bookshop/srv/x-validation.cds
new file mode 100644
index 00000000..3ef7b696
--- /dev/null
+++ b/bookshop/srv/x-validation.cds
@@ -0,0 +1,50 @@
+namespace sap.capire.bookshop;
+using from '../db/schema';
+
+
+/**
+ * Validation constraints for Books
+ */
+view Books.constraints as select from Books { ID,
+
+  // two-step mandatory check
+  title = null ? 'is missing' : trim(title)='' ? 'must not be empty' :
+  null as title,
+
+  // range check
+  stock < 0 ? 'must not be negative' :
+  null as stock,
+
+  // range check
+  price < 0 ? 'must not be negative' :
+  null as price,
+
+  // assert target check
+  genre.ID is not null and not exists genre ? 'does not exist' :
+  null as genre,
+
+  // multiple constraints: mandatory + assert target + special
+  not exists author ? 'Author does not exist: ' || author.ID :
+  author.ID is null ? 'is missing' : // FIXME: expected author.ID to refer to foreign key, apparently that is not the case -> move one line up to see
+  count(author.books.ID) -1 > 1 ? author.name || ' already wrote multiple books, please choose another author' : // TODO: we should support count(author.books)
+  null as author,
+
+} group by ID;
+
+
+
+/**
+ * Validation constraints for Authors
+ */
+view Authors.constraints as select from Authors { ID,
+
+  // two-step mandatory check
+  name = null ? 'is missing' : trim(name)='' ? 'must not be empty' :
+  null as name,
+
+  // constraint related to two fields
+  dateOfDeath > dateOfBirth ? 'date of birth must be before date of death' : null as _born_before_death,
+  $self._born_before_death as dateOfBirth,
+  $self._born_before_death as dateOfDeath,
+
+}

From b55cce3e63dd48a81f8964c1a5ea9ad356208c7e Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Wed, 16 Jul 2025 13:49:45 +0200
Subject: [PATCH 02/11] case when equivalent

---
 bookshop/srv/x-validation.cds | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/bookshop/srv/x-validation.cds b/bookshop/srv/x-validation.cds
index 3ef7b696..c5f67ce1 100644
--- a/bookshop/srv/x-validation.cds
+++ b/bookshop/srv/x-validation.cds
@@ -8,8 +8,12 @@ using from '../db/schema';
 view Books.constraints as select from Books { ID,
 
   // two-step mandatory check
-  title = null ? 'is missing' : trim(title)='' ? 'must not be empty' :
-  null as title,
+  case
+    when title is null  then 'is missing'
+    when trim(title)='' then 'must not be empty'
+  end as title,
+  // the above is equivalent to:
+  // title is null ? 'is missing' : trim(title)='' ? 'must not be empty' :
 
   // range check
   stock < 0 ? 'must not be negative' :

From 7cd3a6d1e327286f6c587469e93f0f829dd7c5b7 Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Wed, 16 Jul 2025 13:59:33 +0200
Subject: [PATCH 03/11] comments

---
 bookshop/srv/x-validation.cds | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/bookshop/srv/x-validation.cds b/bookshop/srv/x-validation.cds
index c5f67ce1..3aeca373 100644
--- a/bookshop/srv/x-validation.cds
+++ b/bookshop/srv/x-validation.cds
@@ -29,12 +29,17 @@ view Books.constraints as select from Books { ID,
 
   // multiple constraints: mandatory + assert target + special
   not exists author ? 'Author does not exist: ' || author.ID :
-  author.ID is null ? 'is missing' : // FIXME: expected author.ID to refer to foreign key, apparently that is not the case -> move one line up to see
-  count(author.books.ID) -1 > 1 ? author.name || ' already wrote multiple books, please choose another author' : // TODO: we should support count(author.books)
+  author.ID is null ? 'is missing' : // FIXME: 1)
+  count(author.books.ID) -1 > 1 ? author.name || ' already wrote too many books' : // TODO: 2)
   null as author,
 
 } group by ID;
 
+// 1) FIXME: expected author.ID to refer to foreign key,
+// apparently that is not the case -> move one line up
+// and run test to see the erroneous impact.
+
+// 2) TODO: we should support count(author.books)
 
 
 /**

From 4fc324c7fb09027200d8b7f48ed9f8e736e16196 Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Wed, 16 Jul 2025 14:08:25 +0200
Subject: [PATCH 04/11] Added instructions for ad-hoc tests in cds repl

---
 bookshop/server.js | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/bookshop/server.js b/bookshop/server.js
index 46467b15..35c74e15 100644
--- a/bookshop/server.js
+++ b/bookshop/server.js
@@ -1,21 +1,28 @@
 //
 //  Quick and dirty implementation for cds.validate() using db-level constraints
+//  Test in cds.repl like that:
+//  await cds.run (()=> INSERT.into (Books, { title:'   ', author_ID:150 }) .then (cds.validate(Books)))
 //
 
 const cds = require('@sap/cds')
 cds.on('served', ()=> {
 
-  const $ = cds.validate; cds.validate = async function (entity, key, ...columns) {
+  const $ = cds.validate; cds.validate = function (entity, key, ...columns) {
+
     if (!entity.is_entity) return $(...arguments)
+    if (!key) return key => cds.validate(entity,key)
+
     if (entity.constraints) entity = entity.constraints
-    if (key?.results) key = key.results[0].lastInsertRowid
-    const checks = await SELECT.one.from (entity, key, columns.length && columns)
-    const failed = {}; for (let c in checks) {
-      if (c in entity.keys) continue
-      if (c[0] == '_') continue
-      if (checks[c]) failed[c] = checks[c]
-    }
-    if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
+    if (key.results) key = key.results[0].lastInsertRowid
+
+    return SELECT.one.from (entity, key, columns.length && columns) .then (checks => {
+      const failed = {}; for (let c in checks) {
+        if (c in entity.keys) continue
+        if (c[0] == '_') continue
+        if (checks[c]) failed[c] = checks[c]
+      }
+      if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
+    })
   }
 
 })

From 04d659c9c24309fc674a297815786a4b6952c77e Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Wed, 16 Jul 2025 17:25:32 +0200
Subject: [PATCH 05/11] more comments

---
 bookshop/srv/x-validation.cds | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/bookshop/srv/x-validation.cds b/bookshop/srv/x-validation.cds
index 3aeca373..8326afd3 100644
--- a/bookshop/srv/x-validation.cds
+++ b/bookshop/srv/x-validation.cds
@@ -28,9 +28,9 @@ view Books.constraints as select from Books { ID,
   null as genre,
 
   // multiple constraints: mandatory + assert target + special
+  author.ID is null ? 'is missing' : // FIXME: 1) // TODO: 2)
   not exists author ? 'Author does not exist: ' || author.ID :
-  author.ID is null ? 'is missing' : // FIXME: 1)
-  count(author.books.ID) -1 > 1 ? author.name || ' already wrote too many books' : // TODO: 2)
+  count(author.books.ID) -1 > 1 ? author.name || ' already wrote too many books' : // TODO: 3)
   null as author,
 
 } group by ID;
@@ -39,7 +39,9 @@ view Books.constraints as select from Books { ID,
 // apparently that is not the case -> move one line up
 // and run test to see the erroneous impact.
 
-// 2) TODO: we should support count(author.books)
+// 2) TODO: we should allow to write author is null instead of author.ID is null
+
+// 3) TODO: we should support count(author.books)
 
 
 /**

From 15fa7de880e0cb907ac02d94c058c8b21a9be6a8 Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Wed, 16 Jul 2025 17:27:07 +0200
Subject: [PATCH 06/11] .

---
 bookshop/srv/x-validation.cds | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bookshop/srv/x-validation.cds b/bookshop/srv/x-validation.cds
index 8326afd3..b92d32a0 100644
--- a/bookshop/srv/x-validation.cds
+++ b/bookshop/srv/x-validation.cds
@@ -54,7 +54,7 @@ view Authors.constraints as select from Authors { ID,
   null as name,
 
   // constraint related to two fields
-  dateOfDeath > dateOfBirth ? 'date of birth must be before date of death' : null as _born_before_death,
+  dateOfDeath > dateOfBirth ? 'we must be born before we die' : null as _born_before_death,
   $self._born_before_death as dateOfBirth,
   $self._born_before_death as dateOfDeath,
 

From d57c29e1267e529e54486890b4de58963cb68242 Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Wed, 23 Jul 2025 17:36:58 +0200
Subject: [PATCH 07/11] constraints on service level

---
 bookshop/server.js              |  22 +++++-
 bookshop/srv/access-control.cds |   2 +-
 bookshop/srv/admin-service.cds  |   2 +-
 bookshop/srv/x-validation.cds   | 135 ++++++++++++++++++--------------
 4 files changed, 95 insertions(+), 66 deletions(-)

diff --git a/bookshop/server.js b/bookshop/server.js
index 35c74e15..819c55b7 100644
--- a/bookshop/server.js
+++ b/bookshop/server.js
@@ -1,19 +1,31 @@
 //
 //  Quick and dirty implementation for cds.validate() using db-level constraints
 //  Test in cds.repl like that:
+//  {Books} = AdminService.entities
 //  await cds.run (()=> INSERT.into (Books, { title:'   ', author_ID:150 }) .then (cds.validate(Books)))
+//  await AdminService.create ('Books', { title:'   ', author_ID:150 })
 //
 
 const cds = require('@sap/cds')
 cds.on('served', ()=> {
 
-  const $ = cds.validate; cds.validate = function (entity, key, ...columns) {
+  const $ = cds.validate
+  cds.validate = function (entity, key, ...columns) {
 
-    if (!entity.is_entity) return $(...arguments)
-    if (!key) return key => cds.validate(entity,key)
+    if (entity?.ref) entity = { // quick and dirty
+      name: entity.ref[0],
+      constraints: { // even quicker and dirtier
+        name: entity.ref[0] +'.constraints',
+        keys: {ID:1}
+      }
+    }
+    else if (!entity.is_entity) return // we skip all standard validations for the experiments
+    else if (!entity.is_entity) return $(...arguments) // eslint-disable-line no-dupe-else-if
 
     if (entity.constraints) entity = entity.constraints
-    if (key.results) key = key.results[0].lastInsertRowid
+    if (!key) return key => cds.validate(entity,key)
+    if (key.results) key = key.results[0].lastInsertRowid // quick and dirty
+    if (key.ID) key = key.ID // quick and dirty
 
     return SELECT.one.from (entity, key, columns.length && columns) .then (checks => {
       const failed = {}; for (let c in checks) {
@@ -25,6 +37,8 @@ cds.on('served', ()=> {
     })
   }
 
+  const { AdminService } = cds.services
+  AdminService.after (['CREATE','UPDATE'], (result,req) =>  cds.validate (req.subject, result))
 })
 
 Object.defineProperties (cds.entity.prototype, {
diff --git a/bookshop/srv/access-control.cds b/bookshop/srv/access-control.cds
index 80384f6e..1cd1ac3c 100644
--- a/bookshop/srv/access-control.cds
+++ b/bookshop/srv/access-control.cds
@@ -1,2 +1,2 @@
 using { AdminService } from './admin-service';
-annotate AdminService with @requires:'admin';
+annotate AdminService with @requires: false; //'admin';
diff --git a/bookshop/srv/admin-service.cds b/bookshop/srv/admin-service.cds
index 37b02eb7..855e73d2 100644
--- a/bookshop/srv/admin-service.cds
+++ b/bookshop/srv/admin-service.cds
@@ -1,6 +1,6 @@
 using { sap.capire.bookshop as my } from '../db/schema';
 service AdminService @(path:'/admin') {
-  entity Authors as projection on my.Authors;
+  entity Authors as projection on my.Authors excluding { books};
   entity Books as projection on my.Books;
   entity Genres as projection on my.Genres;
 }
diff --git a/bookshop/srv/x-validation.cds b/bookshop/srv/x-validation.cds
index b92d32a0..a845caf7 100644
--- a/bookshop/srv/x-validation.cds
+++ b/bookshop/srv/x-validation.cds
@@ -1,61 +1,76 @@
-namespace sap.capire.bookshop;
-using from '../db/schema';
-
-
-/**
- * Validation constraints for Books
- */
-view Books.constraints as select from Books { ID,
-
-  // two-step mandatory check
-  case
-    when title is null  then 'is missing'
-    when trim(title)='' then 'must not be empty'
-  end as title,
-  // the above is equivalent to:
-  // title is null ? 'is missing' : trim(title)='' ? 'must not be empty' :
-
-  // range check
-  stock < 0 ? 'must not be negative' :
-  null as stock,
-
-  // range check
-  price < 0 ? 'must not be negative' :
-  null as price,
-
-  // assert target check
-  genre.ID is not null and not exists genre ? 'does not exist' :
-  null as genre,
-
-  // multiple constraints: mandatory + assert target + special
-  author.ID is null ? 'is missing' : // FIXME: 1) // TODO: 2)
-  not exists author ? 'Author does not exist: ' || author.ID :
-  count(author.books.ID) -1 > 1 ? author.name || ' already wrote too many books' : // TODO: 3)
-  null as author,
-
-} group by ID;
-
-// 1) FIXME: expected author.ID to refer to foreign key,
-// apparently that is not the case -> move one line up
-// and run test to see the erroneous impact.
-
-// 2) TODO: we should allow to write author is null instead of author.ID is null
-
-// 3) TODO: we should support count(author.books)
-
-
-/**
- * Validation constraints for Authors
- */
-view Authors.constraints as select from Authors { ID,
-
-  // two-step mandatory check
-  name = null ? 'is missing' : trim(name)='' ? 'must not be empty' :
-  null as name,
-
-  // constraint related to two fields
-  dateOfDeath > dateOfBirth ? 'we must be born before we die' : null as _born_before_death,
-  $self._born_before_death as dateOfBirth,
-  $self._born_before_death as dateOfDeath,
-
+using { AdminService, sap.capire.bookshop as my } from './admin-service';
+
+extend service AdminService with {
+
+  // entity Books.drafts as projection on AdminService.Books;
+  // @cds.api.ignore view Books.drafts.constraints as select from AdminService.Books.drafts mixin {
+  //   before: Association to my.Books on before.ID = $self.ID;
+  //   base: Association to my.Books on base.ID = $self.ID;
+  // } into { ID, // FIXME: compiler should resolve Books without AdminService prefix
+  //   case
+  //     when title is null  then 'is missing'
+  //     when trim(title)='' then 'must not be empty'
+  //   end as title,
+  //   ...
+  // }
+
+  /**
+   * Validation constraints for Books
+   */
+  @cds.api.ignore view Books.constraints as select from AdminService.Books mixin {
+    base: Association to my.Books on base.ID = $self.ID;
+  } into { ID, // FIXME: compiler should resolve Books without AdminService prefix
+
+    // two-step mandatory check
+    case
+      when title is null  then 'is missing'
+      when trim(title)='' then 'must not be empty'
+    end as title,
+    // the above is equivalent to:
+    // title is null ? 'is missing' : trim(title)='' ? 'must not be empty' :
+
+    // range check
+    stock < 0 ? 'must not be negative' :
+    null as stock,
+
+    // range check
+    price < 0 ? 'must not be negative' :
+    null as price,
+
+    // assert target check
+    genre.ID is not null and not exists genre ? 'does not exist' :
+    null as genre,
+
+    // multiple constraints: mandatory + assert target + special
+    author.ID is null ? 'is missing' : // FIXME: 1) // TODO: 2)
+    not exists author ? 'Author does not exist: ' || author.ID :
+    count(base.author.books.ID) -1 > 1 ? author.name || ' already wrote too many books' : // TODO: 3)
+    null as author,
+
+  } group by ID;
+
+  // 1) FIXME: expected author.ID to refer to foreign key,
+  // apparently that is not the case -> move one line up
+  // and run test to see the erroneous impact.
+
+  // 2) TODO: we should allow to write author is null instead of author.ID is null
+
+  // 3) TODO: we should support count(author.books)
+
+
+  /**
+   * Validation constraints for Authors
+   */
+  view Authors.constraints as select from AdminService.Authors { ID, // FIXME: compiler should resolve Authors without AdminService prefix
+
+    // two-step mandatory check
+    name = null ? 'is missing' : trim(name)='' ? 'must not be empty' :
+    null as name,
+
+    // constraint related to two fields
+    dateOfDeath > dateOfBirth ? 'we must be born before we die' : null as _born_before_death,
+    $self._born_before_death as dateOfBirth,
+    $self._born_before_death as dateOfDeath,
+
+  }
 }

From 65eccfad33551db246b60b0eb757aeb0d0a519be Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Thu, 24 Jul 2025 10:38:43 +0200
Subject: [PATCH 08/11] Moved dynamic constraints in a dedicated folder

---
 bookshop/srv/access-control.cds               |  2 +-
 bookshop/srv/admin-service.cds                |  2 +-
 bookshop/test/dynamic-constraints/readme.md   | 26 +++++++++++++++++++
 .../{ => test/dynamic-constraints}/server.js  |  7 ++---
 .../dynamic-constraints/srv/admin-service.cds |  5 ++++
 .../srv/field-control.cds}                    |  2 +-
 .../dynamic-constraints/srv/validation.cds}   |  0
 7 files changed, 36 insertions(+), 8 deletions(-)
 create mode 100644 bookshop/test/dynamic-constraints/readme.md
 rename bookshop/{ => test/dynamic-constraints}/server.js (82%)
 create mode 100644 bookshop/test/dynamic-constraints/srv/admin-service.cds
 rename bookshop/{srv/x-field-control.cds => test/dynamic-constraints/srv/field-control.cds} (88%)
 rename bookshop/{srv/x-validation.cds => test/dynamic-constraints/srv/validation.cds} (100%)

diff --git a/bookshop/srv/access-control.cds b/bookshop/srv/access-control.cds
index 1cd1ac3c..80384f6e 100644
--- a/bookshop/srv/access-control.cds
+++ b/bookshop/srv/access-control.cds
@@ -1,2 +1,2 @@
 using { AdminService } from './admin-service';
-annotate AdminService with @requires: false; //'admin';
+annotate AdminService with @requires:'admin';
diff --git a/bookshop/srv/admin-service.cds b/bookshop/srv/admin-service.cds
index 855e73d2..37b02eb7 100644
--- a/bookshop/srv/admin-service.cds
+++ b/bookshop/srv/admin-service.cds
@@ -1,6 +1,6 @@
 using { sap.capire.bookshop as my } from '../db/schema';
 service AdminService @(path:'/admin') {
-  entity Authors as projection on my.Authors excluding { books};
+  entity Authors as projection on my.Authors;
   entity Books as projection on my.Books;
   entity Genres as projection on my.Genres;
 }
diff --git a/bookshop/test/dynamic-constraints/readme.md b/bookshop/test/dynamic-constraints/readme.md
new file mode 100644
index 00000000..0ffb974d
--- /dev/null
+++ b/bookshop/test/dynamic-constraints/readme.md
@@ -0,0 +1,26 @@
+## Experimental Dynamic Constraints
+
+This example demonstrates how to use dynamic constraints in a CAP application. It includes a service definition and a test setup to validate the constraints.
+
+
+### Prerequisites
+
+You've setup the [_cap/samples_](https://github.com/sap-samples/cloud-cap-samples) like so:
+
+```sh
+git clone -q https://github.com/sap-samples/cloud-cap-samples cap/samples
+cd cap/samples
+npm install
+```
+
+### Testing
+
+Test like that in `cds.repl` from _cap/samples_ root:
+
+```sh
+cds repl --run bookshop/test/dynamic-constraints
+````
+
+```javascript
+await AdminService.create ('Books', { title:'   ', author_ID:150 })
+```
diff --git a/bookshop/server.js b/bookshop/test/dynamic-constraints/server.js
similarity index 82%
rename from bookshop/server.js
rename to bookshop/test/dynamic-constraints/server.js
index 819c55b7..d7d62fbb 100644
--- a/bookshop/server.js
+++ b/bookshop/test/dynamic-constraints/server.js
@@ -1,9 +1,6 @@
 //
-//  Quick and dirty implementation for cds.validate() using db-level constraints
-//  Test in cds.repl like that:
-//  {Books} = AdminService.entities
-//  await cds.run (()=> INSERT.into (Books, { title:'   ', author_ID:150 }) .then (cds.validate(Books)))
-//  await AdminService.create ('Books', { title:'   ', author_ID:150 })
+// Quick and dirty implementation for cds.validate()
+// using db-level constraints.
 //
 
 const cds = require('@sap/cds')
diff --git a/bookshop/test/dynamic-constraints/srv/admin-service.cds b/bookshop/test/dynamic-constraints/srv/admin-service.cds
new file mode 100644
index 00000000..373501e5
--- /dev/null
+++ b/bookshop/test/dynamic-constraints/srv/admin-service.cds
@@ -0,0 +1,5 @@
+using { AdminService } from '../../../srv/admin-service';
+annotate AdminService with @requires: false;
+extend AdminService.Authors with columns {
+  null as books // to simulate the exclusion of books
+}
diff --git a/bookshop/srv/x-field-control.cds b/bookshop/test/dynamic-constraints/srv/field-control.cds
similarity index 88%
rename from bookshop/srv/x-field-control.cds
rename to bookshop/test/dynamic-constraints/srv/field-control.cds
index 9f96d3ad..3b48b7a3 100644
--- a/bookshop/srv/x-field-control.cds
+++ b/bookshop/test/dynamic-constraints/srv/field-control.cds
@@ -1,5 +1,5 @@
 namespace sap.capire.bookshop;
-using from '../db/schema';
+using from './admin-service';
 
 view Books.field.control as select from Books { ID,
   genre.name == 'Drama' ? 'readonly' :
diff --git a/bookshop/srv/x-validation.cds b/bookshop/test/dynamic-constraints/srv/validation.cds
similarity index 100%
rename from bookshop/srv/x-validation.cds
rename to bookshop/test/dynamic-constraints/srv/validation.cds

From 6dc1da2964325100793fff6d9b9c02a95be32e9a Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Thu, 24 Jul 2025 12:24:11 +0200
Subject: [PATCH 09/11] Reverting removal of cds.service.providers

---
 inspectr/srv/data-service.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/inspectr/srv/data-service.js b/inspectr/srv/data-service.js
index e0a5c776..a9bfc355 100644
--- a/inspectr/srv/data-service.js
+++ b/inspectr/srv/data-service.js
@@ -52,7 +52,7 @@ module.exports = { DataService }
 
 /** @returns {cds.Service} */
 function findDataSource(dataSourceName, entityName) {
-  for (let srv of Object.values(cds.services)) { // all connected services
+  for (let srv of cds.service.providers) { // all connected services
     if (!srv.name)  continue // FIXME intermediate/pending in cds.services ?
     if (dataSourceName === srv.name || entityName.startsWith(srv.name+'.')) {
       log._debug && log.debug(`using ${srv.name} as data source`)

From 991e890ba976d51426f34509bb3f27073a4a328f Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Thu, 24 Jul 2025 13:31:45 +0200
Subject: [PATCH 10/11] cleanup impls

---
 bookshop/test/dynamic-constraints/server.js   | 33 ++-----------------
 .../dynamic-constraints/srv/validation.cds    |  2 +-
 bookshop/test/dynamic-constraints/validate.js | 33 +++++++++++++++++++
 3 files changed, 37 insertions(+), 31 deletions(-)
 create mode 100644 bookshop/test/dynamic-constraints/validate.js

diff --git a/bookshop/test/dynamic-constraints/server.js b/bookshop/test/dynamic-constraints/server.js
index d7d62fbb..9c230857 100644
--- a/bookshop/test/dynamic-constraints/server.js
+++ b/bookshop/test/dynamic-constraints/server.js
@@ -3,41 +3,14 @@
 // using db-level constraints.
 //
 
-const cds = require('@sap/cds')
+const cds = require('@sap/cds'); require('./validate.js')
 cds.on('served', ()=> {
-
-  const $ = cds.validate
-  cds.validate = function (entity, key, ...columns) {
-
-    if (entity?.ref) entity = { // quick and dirty
-      name: entity.ref[0],
-      constraints: { // even quicker and dirtier
-        name: entity.ref[0] +'.constraints',
-        keys: {ID:1}
-      }
-    }
-    else if (!entity.is_entity) return // we skip all standard validations for the experiments
-    else if (!entity.is_entity) return $(...arguments) // eslint-disable-line no-dupe-else-if
-
-    if (entity.constraints) entity = entity.constraints
-    if (!key) return key => cds.validate(entity,key)
-    if (key.results) key = key.results[0].lastInsertRowid // quick and dirty
-    if (key.ID) key = key.ID // quick and dirty
-
-    return SELECT.one.from (entity, key, columns.length && columns) .then (checks => {
-      const failed = {}; for (let c in checks) {
-        if (c in entity.keys) continue
-        if (c[0] == '_') continue
-        if (checks[c]) failed[c] = checks[c]
-      }
-      if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
-    })
-  }
-
   const { AdminService } = cds.services
   AdminService.after (['CREATE','UPDATE'], (result,req) =>  cds.validate (req.subject, result))
 })
 
+
+
 Object.defineProperties (cds.entity.prototype, {
   constraints: { get() { return cds.model.definitions[this.name+'.constraints'] }},
   fields: { get() { return cds.model.definitions[this.name+'.field.control'] }},
diff --git a/bookshop/test/dynamic-constraints/srv/validation.cds b/bookshop/test/dynamic-constraints/srv/validation.cds
index a845caf7..4d733947 100644
--- a/bookshop/test/dynamic-constraints/srv/validation.cds
+++ b/bookshop/test/dynamic-constraints/srv/validation.cds
@@ -68,7 +68,7 @@ extend service AdminService with {
     null as name,
 
     // constraint related to two fields
-    dateOfDeath > dateOfBirth ? 'we must be born before we die' : null as _born_before_death,
+    dateOfDeath < dateOfBirth ? 'we can''t die before we are born' : null as _born_before_death,
     $self._born_before_death as dateOfBirth,
     $self._born_before_death as dateOfDeath,
 
diff --git a/bookshop/test/dynamic-constraints/validate.js b/bookshop/test/dynamic-constraints/validate.js
new file mode 100644
index 00000000..8a93f111
--- /dev/null
+++ b/bookshop/test/dynamic-constraints/validate.js
@@ -0,0 +1,33 @@
+const cds = require('@sap/cds')
+const $super = { validate: cds.validate, skip(){} }
+
+
+/**
+ * Quick and dirty implementation for cds.validate() using db-level constraints.
+ */
+cds.validate = function (x, pk, ...columns) {
+
+  // Delegate to base impl of cds.validate() for standard input validation
+  if (!_is_constraints(x)) return $super.skip (...arguments)
+
+  // Support subject refs to base entities as arguments
+  if (x?.ref) [ x, pk ] = [ x.ref +'.constraints', pk.ID||pk ]
+
+  // Run the constraints check query
+  const constraints = cds.model.definitions[x] || cds.error `No such constraints view: ${x}`
+  return SELECT.one.from (constraints, pk, columns.length && columns)
+
+  // Collect and throw errors, if any
+  .then (checks => {
+    const failed = {}; for (let c in checks) {
+      if (c in constraints.keys) continue
+      if (c[0] == '_') continue
+      if (checks[c]) failed[c] = checks[c]
+    }
+    if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
+  })
+}
+
+
+// Helpers
+const _is_constraints = x => x.ref || x.is_entity || typeof x === 'string'

From 4e76d71defeccf1159b9e859db9cb705b4c1aae3 Mon Sep 17 00:00:00 2001
From: Daniel Hutzel <daniel.hutzel@sap.com>
Date: Thu, 24 Jul 2025 13:52:01 +0200
Subject: [PATCH 11/11] polishing

---
 bookshop/test/dynamic-constraints/readme.md             | 4 ++++
 bookshop/test/dynamic-constraints/srv/admin-service.cds | 2 ++
 bookshop/test/dynamic-constraints/validate.js           | 9 +++++----
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/bookshop/test/dynamic-constraints/readme.md b/bookshop/test/dynamic-constraints/readme.md
index 0ffb974d..6660d649 100644
--- a/bookshop/test/dynamic-constraints/readme.md
+++ b/bookshop/test/dynamic-constraints/readme.md
@@ -22,5 +22,9 @@ cds repl --run bookshop/test/dynamic-constraints
 ````
 
 ```javascript
+await AdminService.create ('Books', {})
 await AdminService.create ('Books', { title:'   ', author_ID:150 })
+await AdminService.create ('Books', { title:'x' })
+await cds.validate (Books.constraints, 201)
+await cds.validate (Books.constraints)
 ```
diff --git a/bookshop/test/dynamic-constraints/srv/admin-service.cds b/bookshop/test/dynamic-constraints/srv/admin-service.cds
index 373501e5..fd771d06 100644
--- a/bookshop/test/dynamic-constraints/srv/admin-service.cds
+++ b/bookshop/test/dynamic-constraints/srv/admin-service.cds
@@ -1,3 +1,5 @@
+namespace AdminService; //> for cds.entities
+
 using { AdminService } from '../../../srv/admin-service';
 annotate AdminService with @requires: false;
 extend AdminService.Authors with columns {
diff --git a/bookshop/test/dynamic-constraints/validate.js b/bookshop/test/dynamic-constraints/validate.js
index 8a93f111..22907005 100644
--- a/bookshop/test/dynamic-constraints/validate.js
+++ b/bookshop/test/dynamic-constraints/validate.js
@@ -14,18 +14,19 @@ cds.validate = function (x, pk, ...columns) {
   if (x?.ref) [ x, pk ] = [ x.ref +'.constraints', pk.ID||pk ]
 
   // Run the constraints check query
-  const constraints = cds.model.definitions[x] || cds.error `No such constraints view: ${x}`
-  return SELECT.one.from (constraints, pk, columns.length && columns)
+  const constraints = typeof x === 'string' ? cds.model.definitions[x] || cds.error `No such constraints view: ${x}` : x
+  return SELECT.from (constraints, pk, columns.length && columns)
 
   // Collect and throw errors, if any
-  .then (checks => {
+  .then (rows => (rows.map ? rows : [rows]).map (checks => {
     const failed = {}; for (let c in checks) {
       if (c in constraints.keys) continue
       if (c[0] == '_') continue
       if (checks[c]) failed[c] = checks[c]
     }
     if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
-  })
+    return checks
+  }))
 }