diff --git a/tests/dynamic-constraints/fts/some-feature.cds b/tests/dynamic-constraints/fts/some-feature.cds
new file mode 100644
index 0000000..263f572
--- /dev/null
+++ b/tests/dynamic-constraints/fts/some-feature.cds
@@ -0,0 +1,5 @@
+using { sap.ariba.buying.Requisitions } from '../srv/etc/requisition';
+
+annotate Requisitions with {
+  buyer @assert: (buyer is null ? 'is missing' : null);
+}
diff --git a/tests/dynamic-constraints/readme.md b/tests/dynamic-constraints/readme.md
new file mode 100644
index 0000000..baf76ad
--- /dev/null
+++ b/tests/dynamic-constraints/readme.md
@@ -0,0 +1,37 @@
+## 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/capire/samples) like so:
+
+```sh
+git clone -b dynamic-constraints -q https://github.com/capire/samples cap/samples
+cd cap/samples
+npm install
+```
+
+### Testing
+
+Test like that in `cds.repl` from _cap/samples_ root:
+
+```sh
+cds repl --run tests/dynamic-constraints
+````
+
+```js
+await AdminService.create ('Books', {})
+await AdminService.create ('Books', { title:'   ', author_ID:150 })
+await AdminService.create ('Books', { title:'x' })
+```
+
+```js
+await cds.validate (Books.constraints, 201)
+await cds.validate (Books.constraints)
+```
+
+```js
+await AdminService.read `ID, title, price, fc.price from Books`
+```
diff --git a/tests/dynamic-constraints/server.js b/tests/dynamic-constraints/server.js
new file mode 100644
index 0000000..c833857
--- /dev/null
+++ b/tests/dynamic-constraints/server.js
@@ -0,0 +1,17 @@
+//
+// Quick and dirty implementation for cds.validate()
+// using db-level constraints.
+//
+
+const cds = require('@sap/cds'); require('./validate.js')
+cds.on('served', ()=> {
+  const { AdminService } = cds.services
+  AdminService.after (['CREATE','UPDATE'], (_,req) =>  cds.validate (req))
+})
+
+
+
+Object.defineProperties (cds.entity.prototype, {
+  constraints: { get() { return cds.model.definitions[this.name+'.constraints'] }},
+  controls: { get() { return cds.model.definitions[this.name+'.field.control'] }},
+})
diff --git a/tests/dynamic-constraints/srv/admin-service.cds b/tests/dynamic-constraints/srv/admin-service.cds
new file mode 100644
index 0000000..25b1460
--- /dev/null
+++ b/tests/dynamic-constraints/srv/admin-service.cds
@@ -0,0 +1,14 @@
+using { AdminService } from '@capire/bookshop';
+namespace AdminService; //> for cds.entities
+
+annotate AdminService with @odata.draft.enabled;
+annotate AdminService with @requires: false;
+
+extend AdminService.Authors with columns {
+  // null as books // to simulate the exclusion of books
+}
+
+// Should be provided by CAP ootb:
+extend AdminService.Books with columns {
+  active : Association to AdminService.Books on active.ID = $self.ID,
+}
diff --git a/tests/dynamic-constraints/srv/etc/catalog.cds b/tests/dynamic-constraints/srv/etc/catalog.cds
new file mode 100644
index 0000000..3a8cea2
--- /dev/null
+++ b/tests/dynamic-constraints/srv/etc/catalog.cds
@@ -0,0 +1,20 @@
+using { cuid, Currency } from '@sap/cds/common';
+
+context sap.ariba.catalog {
+
+  entity Product : cuid { // = ProductDescription in Ariba CG
+    name : String(111);
+    descr : String(1111);
+    price : Decimal(10,2);
+    stock : Integer;
+    suppliers : Association to many Suppliers;
+  }
+
+  entity Suppliers : cuid {
+    name : String(111);
+    contact : String(111);
+    address : String(1111);
+    currency : Currency;
+  }
+
+}
diff --git a/tests/dynamic-constraints/srv/etc/requisition.cds b/tests/dynamic-constraints/srv/etc/requisition.cds
new file mode 100644
index 0000000..30cb706
--- /dev/null
+++ b/tests/dynamic-constraints/srv/etc/requisition.cds
@@ -0,0 +1,31 @@
+
+using { cuid } from '@sap/cds/common';
+using { sap.ariba.catalog.Product, sap.ariba.catalog.Suppliers } from './catalog';
+
+type Price : Decimal(10,2);
+
+context sap.ariba.buying {
+
+  entity Requisitions : cuid {
+    buyer : String;
+    Items : Composition of many LineItems on Items.parent = $self;
+    totalPrice : Price;
+  }
+
+  entity LineItems {
+    key parent : Association to Requisitions;
+    key pos  : Integer;
+    product  : Association to Product;
+    supplier : Association to Suppliers; //
+    quantity : Integer;
+    // supplierCurrency : Currency;
+  };
+
+  // entity Product : sap.ariba.catalog.Product {
+  //   product : Association to Product;
+  // }
+  entity Suppliers : sap.ariba.catalog.Suppliers {
+    product : Association to Product;
+  }
+
+}
diff --git a/tests/dynamic-constraints/srv/etc/some-body-else.cds b/tests/dynamic-constraints/srv/etc/some-body-else.cds
new file mode 100644
index 0000000..6806745
--- /dev/null
+++ b/tests/dynamic-constraints/srv/etc/some-body-else.cds
@@ -0,0 +1,16 @@
+using { sap.ariba.buying } from './requisition';
+context other {
+
+  aspect managed {
+    createdBy: User @assert: (createdBy is not null ? null : 'is missing');
+    createdAt: DateTime;
+    lastModifiedBy: User;
+    lastModifiedAt: DateTime;
+  }
+
+  type User : String;
+
+  extend buying.Requisitions with managed;
+  extend buying.Suppliers with managed;
+
+}
diff --git a/tests/dynamic-constraints/srv/etc/validation-aspects.cds b/tests/dynamic-constraints/srv/etc/validation-aspects.cds
new file mode 100644
index 0000000..5b93d5d
--- /dev/null
+++ b/tests/dynamic-constraints/srv/etc/validation-aspects.cds
@@ -0,0 +1,36 @@
+using { sap.capire.bookshop.Books } from '@capire/bookshop';
+
+
+/**
+ * Validation constraints for Books
+ */
+@validations aspect AdminService.Books.constraints.aspect : Books {
+
+  // two-step mandatory check
+  check_title = case
+    when title is null  then 'is missing'
+    when trim(title)='' then 'must not be empty'
+  end;
+
+  check_title2 = (
+    title is null ? 'is missing' :
+    trim(title)='' ? 'must not be empty' : null
+  );
+
+  // range check
+  check_stock = stock < 0 ? 'must not be negative' : null;
+
+  // range check
+  check_price = price < 0 ? 'must not be negative' : null;
+
+  // assert target check
+  // check_genre = genre is not null and not exists genre ? 'does not exist' : null;
+
+  // multiple constraints: mandatory + assert target + special
+  check_author = case
+    when author.ID is null then 'is missing' // FIXME: 1) // TODO: 2)
+    // when not exists author then 'Author does not exist: ' || author.ID
+    when count(author.books.ID) -1 > 1 then author.name || ' already wrote too many books' // TODO: 3)
+    when /* exists */ author.books[genre.name like '%Noire%'] then 'Author has written a Noire book'
+  end
+}
diff --git a/tests/dynamic-constraints/srv/etc/validation-asserts.cds b/tests/dynamic-constraints/srv/etc/validation-asserts.cds
new file mode 100644
index 0000000..c4eb087
--- /dev/null
+++ b/tests/dynamic-constraints/srv/etc/validation-asserts.cds
@@ -0,0 +1,72 @@
+using { sap.capire.bookshop.Books } from '@capire/bookshop';
+
+// @mandatory
+// @readonly
+// @hidden @visible @inapplicable
+
+// @assert.range
+// @assert.format
+// @assert.target
+
+// Following are invariant constraints declared on domain model entity
+annotate Books with {
+
+  // manual two-step mandatory constraint
+  // title @assert.constraint: {
+  //   not_null: { condition: (title is not null), message: 'is missing' },
+  //   not_empty: { condition: (trim(title) != ''), message: 'must not be empty' },
+  // };
+
+  // manual two-step mandatory constraint
+  title @assert: (case
+    when title is null  then 'is missing'
+    when trim(title)='' then 'must not be empty'
+  end);
+
+  // range check
+  stock @assert: (case
+    when stock <= 0 then 'must not a positive number'
+  end);
+
+  // range check
+  price @assert: (case
+    // when price is not null and not price between 0 and 500 then 'must be between 0 and 500'
+    when price <= 0 or price > 500 then 'must be between 0 and 500'
+  end);
+
+  // assert target check
+  // genre @assert: (case
+  //   when genre is not null and not exists genre then 'does not exist'
+  // end);
+
+  genre @assert: (case
+    when genre is null then null // genre may be null
+    when not exists genre then 'does not exist'
+  end);
+
+  // multiple constraints: mandatory + assert target, ...
+  author @assert: (case
+    when author is null then 'is missing'
+    when not exists author then 'does not exist'
+  end);
+}
+
+
+// Following need to go on service-level entity, as rewriting would fail for CatalogService
+annotate AdminService.Books with {
+
+  // ... + special
+  author @assert: (case
+    when sum(author.books.price) > 111 then author.name || ' already earned too much with their books'
+    when count(author.books.ID) -1 > 1 then author.name || ' already wrote too many books'
+    // FIXME: ^^^^^^^^^^^^^^^^ cqn4sql doesn't support count(author.books) yet
+  end);
+
+  price @mandatory: (exists author.books.genre[name = 'Drama']);
+
+  price @assert: (case
+    when price is null and exists author.books.genre[name = 'Drama']
+    then 'Price must be specified for books by drama queens'
+  end);
+
+}
diff --git a/tests/dynamic-constraints/srv/etc/validation-views.cds b/tests/dynamic-constraints/srv/etc/validation-views.cds
new file mode 100644
index 0000000..b390cee
--- /dev/null
+++ b/tests/dynamic-constraints/srv/etc/validation-views.cds
@@ -0,0 +1,80 @@
+using { AdminService, sap.capire.bookshop as my } from '../admin-service';
+
+// 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
+ */
+@validation view AdminService.Books.constraints as select from AdminService.Books mixin {
+  base: Association to my.Books on base.ID = $self.ID // Should be provided by CAP ootb
+} into {
+  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,
+
+  genre.name as _genre,
+
+  // multiple constraints: mandatory + assert target + special
+  case
+    when author.ID is null then 'is missing' // FIXME: 1) // TODO: 2)
+    when not exists author then 'Author does not exist: ' || author.ID
+    when sum(base.author.books.price) > 111 then author.name || ' already earned too much' // TODO: 3)
+  end as author,
+
+} group by ID; // because of the count(base.author.books) above
+
+// 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
+ */
+@validation view AdminService.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 can''t die before we are born' : null as _born_before_death, // reuse condition
+  $self._born_before_death as dateOfBirth,
+  $self._born_before_death as dateOfDeath,
+
+}
+
+
+annotate AdminService.Books.constraints with @cds.api.ignore @odata.draft.enabled: false;
diff --git a/tests/dynamic-constraints/srv/field-control.cds b/tests/dynamic-constraints/srv/field-control.cds
new file mode 100644
index 0000000..37d3af9
--- /dev/null
+++ b/tests/dynamic-constraints/srv/field-control.cds
@@ -0,0 +1,11 @@
+using { AdminService } from './admin-service';
+
+@fieldcontrol view AdminService.Books.field.control as select from AdminService.Books { ID,
+  genre.name == 'Drama' ? 'readonly' :
+  null as price
+}
+
+// Make that available to Fiori clients
+extend AdminService.Books with columns {
+  fc : Association to AdminService.Books.field.control on fc.ID = $self.ID
+}
diff --git a/tests/dynamic-constraints/srv/validation.cds b/tests/dynamic-constraints/srv/validation.cds
new file mode 100644
index 0000000..be0b242
--- /dev/null
+++ b/tests/dynamic-constraints/srv/validation.cds
@@ -0,0 +1 @@
+using from './etc/validation-asserts';
diff --git a/tests/dynamic-constraints/validate.js b/tests/dynamic-constraints/validate.js
new file mode 100644
index 0000000..4867dc4
--- /dev/null
+++ b/tests/dynamic-constraints/validate.js
@@ -0,0 +1,63 @@
+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 (req) {
+  if (req.is_entity) {
+    const asserts = _collect_asserts4 (req); if (!asserts.length) return
+    const vq = SELECT.from (req) .columns (asserts)
+    return vq .then (_handle_results)
+  }
+  if (req instanceof cds.Request === false) return // $super.validate (...arguments)
+  const vq = _validation_query4 (req)
+  return vq .then (_handle_results)
+}
+
+function _validation_query4 (req) {
+  let pk = _key_from_data (req)
+  let constraints = cds.model.definitions [req.target.name + '.constraints']
+  if (constraints) {
+    const asserts = constraints.query.columns .filter (c => c.as[0] !== '_' && !((c.as || c.ref[0]) in pk))
+    return SELECT.from (constraints, pk) .columns (asserts)
+  } else {
+    const asserts = _collect_asserts4 (req.target)
+    return SELECT.from (req.target, pk) .columns (asserts)
+  }
+}
+
+function _collect_asserts4 (entity) {
+  const cols = []
+  for (let e of entity.elements) {
+    if (e.$struct) continue // skip structured elements
+    let xpr = _asserts4 (e)
+    if (xpr) cols.push({ xpr, as: e.name })
+  }
+  return cols
+}
+
+function _asserts4 (e) {
+  let xpr = e?.['@assert']?.xpr; if (!xpr) return
+  let inherited = _asserts4 (e.parent.__proto__.elements?.[e.name])
+  if (inherited) xpr = [ ...inherited.slice(0,-1), ...xpr.slice(1) ]
+  return xpr
+}
+
+function _handle_results (rows) {
+  if (!Array.isArray(rows)) rows = [rows]
+  return rows.map (checks => {
+    const failed = {}; for (let c in checks)
+      if (checks[c]) failed[c] = checks[c]
+    if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
+    return checks
+  })
+}
+
+function _key_from_data (req) {
+  const pk = {}
+  for (let k in req.target.keys)
+    if (k in req.data) pk[k] = req.data[k]
+  return pk
+}
\ No newline at end of file