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Learn how to define constraints declaratively in your CDS model
Constraints expressed in the model rather than checked in a handler — the distinction the atlas draws between input validation the framework enforces and validation somebody writes.
Where it sits
Explains
Input validationCAPInput validationRejecting bad input before it reaches the database. While this can be done manually inside a handler, there are solutions in place to derive type, range, enum and mandatory checks from the model definitions.Data modellingCAPData modellingDefining the shape of data before anything serves it: entities and their types, how they relate, and the projections and views that services and applications consume.
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For input-validation
Applies in
For data-modelling
Applies in
Group by22 of 22 pieces
Piece, what it offersStill applies
Deep Insert in SAP CAPM Using Composition and Fiori ElementsDeep Insert in SAP CAPM Using Composition and Fiori ElementsParent and children created in one transaction, which composition already gives you in the model — the post is about what Fiori elements does with it, and what the payload looks like when the UI sends both at once.published 2026-05-22
Declarative Programming in CAP: Less Code, More ValueDeclarative Programming in CAP: Less Code, More ValueAn argument for annotations over handlers, made from the case where it is most obvious: repetitive validation logic that could be declared instead of written. Describes what you want rather than how to get it, and lets the runtime decide the how.published 2026-02-05
Building an Enterprise Application Using Fiori Elements and CAP - Part 1Building an Enterprise Application Using Fiori Elements and CAP - Part 1Part one of three, and it is all backend: the CAP service the UI will sit on. The author states the constraint the series works under — simple enough for someone new to the stack, without departing from the standard project layout.Farooq, published 2025-12-10
Create CDS Views and expose through OData service in CAPMCreate CDS Views and expose through OData service in CAPMViews defined in CDS and then exposed, which is the whole of what a small CAP service is. Written step by step from cds init onward in Business Application Studio.VenkateshMundru, published 2025-08-11
A CAP Plugin for Flexible Number Range Management: cds-numberrange-pluginA CAP Plugin for Flexible Number Range Management: cds-numberrange-pluginThe author's own plugin, and the reason given for writing it is about plugins rather than about number ranges: a year of using them convinced them that this was the way to extend CAP without leaving marks on the application. Sequential document numbers are the thing it does; keeping the host project clean is the thing it argues for.abdulbasit, published 2025-06-17
Understanding Projections in CAPM: Select Only What You Need!Understanding Projections in CAPM: Select Only What You Need!One concept, explained by someone who had just learned it and says so — what a projection is, why it matters, and an analogy. The register is unusual here and suits the subject: projections are the first thing that makes CDS feel different from a table.Avisek_, published 2025-06-10
CAPVAL: A project is bornCAPVAL: A project is bornThis second CAPVAL post announces CAPVAL version 2.0, made compatible with CAP v8 after breaking changes there, with the fix shown as a custom cds.middlewares.after error handler. It restates the plugin's @validation.message annotation alongside standard annotations such as @mandatory as the input validation mechanic the project builds on, and the release otherwise adds automated tests and release-automation GitHub Actions rather than new annotations.published 2024-08-26
CAP, CDS, CDL, CSN and jq - finding associationsCAP, CDS, CDL, CSN and jq - finding associationsHow associations are actually represented once CDL is compiled into CSN, worked out by parsing the machine-readable form with jq. Useful less as a recipe than as a way in: anything that wants to reason about a CDS model without the compiler has to read CSN, and this is what that looks like from the outside.published 2024-04-16
Extend SAP Cloud Application Programming Model(CAP) Validations with the CAPVAL PluginExtend SAP Cloud Application Programming Model(CAP) Validations with the CAPVAL PluginThe complaint first: the built-in annotations are good for data integrity and poor at telling the user what went wrong, and there is no way to reuse a rule. capval, the plugin the post announces, adds @validation.message alongside the standard annotations rather than replacing them, and @validation.handler for a check written as a class. Published in January 2024, before the 1.2.0 line the README now pairs with @sap/cds 8.0.0 and above; the two annotations it shows are the two the README still documents.published 2024-01-09
SAP CAP(Cloud Application Programming)开发框架概述SAP CAP(Cloud Application Programming)开发框架概述A Chinese-language walkthrough of CAP built mainly from CAPire's own "About CAP" page: CDS entities, associations, compositions and aspects for data modelling, with an extend Books with @restrict: [{ grant:'WRITE', to:'admin' }] aspect as its authorization example; CQL and CQN queries shown against both a local service and OData's $select/$expand; and the service-and-event model — this.on, this.emit, srv.on — that carries CAP's async processing. It closes with the author's own setup: installing @sap/cds-dk, scaffolding a bookshop project with cds init, and running it with cds watch against local SQLite, mocked authentication and file-based messaging standing in for HANA Cloud, IAS and Kafka.ArthurYang, published 2024-01-07
#CAP-TechBytes Input Validation#CAP-TechBytes Input ValidationThe annotations one at a time — @mandatory, @assert.unique, @assert.range including the enum form, @assert.format — each with what it produces. Ends on error handling, which is the part that decides whether any of it is usable from a UI.Thajunniza, published 2023-07-07
[Part - 1] Enrich CAP based Services with Behaviors using Annotations[Part - 1] Enrich CAP based Services with Behaviors using AnnotationsWalks through CDS annotations that add behaviour beyond CRUD: @readonly and @insertonly take away write, update or delete on an entity or element, each shown with the OData metadata it generates. @mandatory, @assert.unique, @assert.integrity, @assert.format and @assert.range then enforce input checks that @sap/cds runs on write, with the SQL or HANA constraint @assert.unique compiles to and the error code each rejection returns. It names @restrict and @requires but defers them, calling authorization too large a topic for this post.published 2023-01-28
SAP CAP Recent Enhancements the HANA Dev Should Know AboutSAP CAP Recent Enhancements the HANA Dev Should Know AboutThomas Jung walks through CAP features for HANA database developers that landed through late 2021: doc comments in the data model (CDL comments propagated into generated database objects via the package.json cdsc.docs compiler option), and schema evolution reaching general availability in the November 2021 release, using the @cds.persistence.journal annotation and cds.hana.journal settings to generate incremental hdbmigrationtable migration scripts instead of dropping and recreating tables. It also walks through two features outside those two: window functions in view column definitions, added in the December 2021 release, and a beta assert_integrity setting that generates database foreign-key constraints from 1:1 associations and compositions.published 2022-02-15
SAP CAP Adapter to expose OData as custom REST ServiceSAP CAP Adapter to expose OData as custom REST ServiceWalks through consuming an external OData V2 service in a CAP project — cds import converts the Northwind service's EDMX into a CSN and cds.connect.to wires up the remote proxy — then re-exposing it as plain REST with the @protocol:'rest' annotation instead of OData's own envelope. Shows two ways to reshape the response, renaming and dropping fields in a CDS projection or rewriting the returned objects in a custom service handler, and remaps ?pageSize and ?offset onto OData's $top and $skip in that same handler.Former Member, published 2021-09-15
Creating structured types, enums and named aspects using the CDS Graphical ModelerCreating structured types, enums and named aspects using the CDS Graphical ModelerThe modelling constructs that are awkward to draw — structured types, enums, named aspects — done in the graphical modeller rather than in CDL.Xiao-fei_Song, published 2021-05-26
Importing @sap/cds common.cds to your CAP project using the CDS Graphical ModelerImporting @sap/cds common.cds to your CAP project using the CDS Graphical ModelerPulling the common aspects and code lists from @sap/cds into a model through the modeller, so the reuse types appear in the diagram rather than only in the file.Xiao-fei_Song, published 2021-05-06
First Java Cap ApplicationFirst Java Cap ApplicationA step-by-step walkthrough of a first CAP Java project: com.sap.cds:cds-services-archetype scaffolds the initial Maven project, and the domain model is then rewritten in the db folder with entities, the cuid and managed aspects, associations, compositions and a CodeList, so a hand-coded event handler serving a single entity gives way to a service that CAP's generic persistence handling serves without custom code. It deploys that model to SQLite for local development — cds deploy --to sqlite, then a Spring profile pointing at the generated database file — and ends by adding an index.cds so the model and service can be published as a reusable npm module.bruce_wang3, published 2020-12-08
Computed field example in CAPComputed field example in CAPAn answer to a Community question — how to count the entities on the far side of an association — written up as a short post rather than left in a thread. The answer combines CDS with Node.js service events, which is the seam worth noticing: some of what looks like modelling is expressed in the model and some has to be computed when the request arrives, and the boundary between them is not obvious from either side.published 2019-08-21
Computed field example in CAP
Data modelling has changed 3 times since this was published, most recently in @sap/cds 9.9.0, 2026-04-23. Affects A recipe, Runnable code.
SAP Cloud Platform Backend service: Tutorial [11]: CDS : magic: key: generationSAP Cloud Platform Backend service: Tutorial [11]: CDS : magic: key: generationExplains CDS's UUID key type: giving a key property UUID gets its value generated automatically instead of a hand-picked unused number, as data modelling lets an element's type do, at the cost of a 36-character value unfit for a user-facing display. It then works out how that generated value is addressed in a single-entity read URL — bare brackets in OData V4 against the guid'...' literal V2 requires — citing the OData specification for the difference.CarlosRoggan, published 2019-03-15
Develop a full stack Business application with SAP Cloud Application Programming ModelDevelop a full stack Business application with SAP Cloud Application Programming ModelBuilds a full-stack CAP application in SAP Web IDE Full Stack's now-retired 'SAP Cloud Platform Business Application' template: a data-model.cds entity with its own service definition, then Fiori annotations on the generated OData. Building the project compiles that model into Catalog.xml and csn.json, the EDMX and CSN that metadata publishing says every exposed service gets. The entity and service definitions it writes by hand are the basic shape data modelling covers, though the webIDE and MTA tooling staged around them is gone.former_member584731, published 2018-11-29
Everything new: Try out the latest features in CAPEverything new: Try out the latest features in CAPCAP (@sap/cds) gains the features this hands-on session works through: declarative constraints, which is the input validation concern, status flows as status transition flows, a cds REPL, extensibility through @sap/cds-oyster, and HCQL, which SAP's abstract calls CAP's native query-over-HTTP protocol, after an opening stretch of AI-driven app development. The abstract names the features and stops there; what each one does is not described. A TechEd 2026 hands-on session (Wednesday 28 October, Berlin), presented by Daniel Hutzel, Daniel Schlachter, Marc Huber and Tim Back, written here from SAP's abstract; the recording is not yet published.
Analyze and optimize ABAP Cloud model apps built on core data servicesAnalyze and optimize ABAP Cloud model apps built on core data servicesPerformance anti-patterns in data models built with ABAP CDS under ABAP Cloud applications, and the tools that find them: the abstract names ABAP cross trace, the SQL analyzer (PlanViz) in Visual Studio Code and the SAP HANA database explorer as what the session uses to follow a bottleneck from the application to the database. The anti-patterns are taken from real business applications, which is where the data modelling edge holds; which ones are shown is not in the abstract. A TechEd 2026 session (Tuesday 27 October, Berlin), presented by Ingo Braeuninger, Robert Werlich, Steffen Siegmund and Thomas Fiedler, written here from SAP's abstract; the recording is not yet published.
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Input validationcapability, core and community
Data modellingcapability, core and community
SAP Developer Centerpublishing source
SAP Developer Centergraphql
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Type
tutorial
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developers.sap.com
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History
- explains → applies_to on capability:input-validation (cap); capability:data-modelling (cap)Door scope proposed from the title and summary, so a door page lists the piece only where it holds (docs/concepts/content-on-doors.md).
- Entered the atlasDiscovered via SAP Developer Center · graphql.
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