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Computed field example in CAP
An 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.
Where it sits
Explains
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.
Since then
Data modelling has changed 3 times since this was published, most recently in @sap/cds 9.9.0, 2026-04-23
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DJ AdamsDJ AdamsWrote this
Developer Advocate
In the atlas: contributes to 20, wrote 22@qmacroauthor
Developer Advocate
In the atlas: contributes to 20, wrote 22@qmacroauthor
Before you read it
read from the pageApplicabilityCore changedData modelling has changed 3 times since this was published, most recently in @sap/cds 9.9.0, 2026-04-23.
This is a derived prompt to re-check the work, not a claim that the work is wrong. Exact stale statements are recorded separately after editorial review.
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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
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
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
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
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
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
Learn how to define constraints declaratively in your CDS modelLearn how to define constraints declaratively in your CDS modelConstraints 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.SAP
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.
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
CAP in the age of AI #7 - vector embeddings wrap-upCAP in the age of AI #7 - vector embeddings wrap-upThe same embeddings model taken from SQLite to SAP HANA Cloud, then handed to an agent. Locally it is @cap-js/ai that adds the vector functions SQLite lacks and downloads an all-MiniLM L6v2 ONNX model on first start; on HANA natural language processing has to be switched on, the model name is a mandatory argument, the vectors it returns are 768 dimensions, and dimensions must match on both sides of a comparison. HANA itself can be given SAP AI Core as a remote source for other embedding models, which a CDS.ql expression has to inject because the postfix notation only takes what the CDS model holds, and the hour ends with a search function over cosine similarity exposed over @cap-js/mcp, so an agent asked about low output from solar panels calls semantic search instead of writing the query itself.published 2026-10-16
CAP in the age of AI #6 - vector embeddingsCAP in the age of AI #6 - vector embeddingsVector embeddings put to work in the incident management sample, answering whether this problem has been seen before. An embedding element of type Vector is calculated and stored from the vector_embedding function, so the database refreshes it whenever the text behind it changes, and cosine_similarity compares it with a freshly embedded string; because a title says little, a scheduled action first summarises each incident's conversation through a model on SAP AI Core and the embedding is taken from that summary. The similar-incidents list is a view joining incidents to themselves, with order and limit set in a before handler on the expanded query, and the vector element excluded from the service, since OData knows nothing about vectors — on SAP HANA Cloud the function is native, while SQLite needs packages added to the project.published 2026-10-09
Custom Business Logic Extensibility in CAP (CDS-Oyster)Custom Business Logic Extensibility in CAP (CDS-Oyster)A Devtoberfest 2026 session walking @sap/cds-oyster — at version 0.55, with 1.0 stated for Q4 — end to end on a multitenant xtravels, from the application developer's side and the extension developer's side. The application developer adds a submit-for-review action to the status flow and opens exactly one surface for custom code: a separate extension service marked as extensible code, holding a no-op validate action and two read-only helper entities, which the host application calls before the status change; nothing else is extensible, because the annotation defaults to false. The extension developer works in a project whose base model came from cds pull, with test data, a server.js and types from @cap-js/cds-typer added so the UI and code completion work, debugs the handler locally and pushes it as an @sap/cds-mtxs extension, after which the next request rejects a travel over the policy limit without a restart — the code having been stored as an annotation in the tenant's model and run in a Rust WebAssembly sandbox with no database connection, whose queries go back to the CAP runtime as CQL strings, which is tenant extensibility extended from fields to logic.published 2026-10-09
CAP in the age of AI #5 - agents wrap-upCAP in the age of AI #5 - agents wrap-upThe agents topic closed out on what sits around the agent rather than inside it, now that the documentation has moved into capire. The chat preview's session is persisted in the database rather than kept in memory, traces go out through @cap-js/telemetry to a self-hosted MLflow under the OpenTelemetry conventions for generative AI, and the panel is explicit that @agent reuses the MCP adapter's code programmatically without serving an MCP endpoint. It ends in the xtravels sample, where a travel agent delegates to a hotel-service sub-agent and reaches a separately started flight service over MCP through the service binding CAP resolves anyway. Earlier in the hour the same agent answers from a model running on the presenter's laptop, reached as an OpenAI-compatible endpoint.published 2026-10-02
What's in Daniel Hutzel's brain?What's in Daniel Hutzel's brain?A Devtoberfest 2026 session in the building-apps track, in which Daniel Hutzel and DJ Adams work through what the CAP team is building for agents. A bookshop gets an MCP endpoint beside its OData one from a single annotation, with the plugin writing the coding agent's configuration itself; in the xt-travels sample five services that know nothing about each other are served over MCP and an agent does the orchestration the hand-built UI and its value helps used to do. Hutzel then annotates a service as an agent so the ReAct loop and the choice of model move into the CAP service, and finally drops MCP for a skill that teaches the agent CQL instead, which is where the edges to Serve your application over MCP, Agent tooling and Agent guidance come from. The mechanism under all of it, a plugin file in the package root and event handlers that can be added to any CAP service, is the edge to Plugin authoring.published 2026-10-02
CAP in the age of AI #4 - more on agentsCAP in the age of AI #4 - more on agentsAsking a human first, and telling the agent how to behave. Ordering a book through @cap-js/agents happens without a question being asked; the human-in-the-loop annotation on the action turns the same request into an approve-or-reject step, which the episode follows down to the A2A status update that stores the task in an input-required state in the database — A2A itself being JSON-RPC 2.0 over HTTP with server-sent events for the stream. The rest is instructions on disk: an agents.md in the service's own folder removes the question about how many copies to order, a skill under a skills folder is advertised by its description and read only when the agent decides the case applies, and either file makes the plugin build a deep agent instead of the plain one.published 2026-09-11
CAP in the age of AI #3 - from MCP to A2ACAP in the age of AI #3 - from MCP to A2AThe episode that finishes @cap-js/mcp with authorisation and then crosses to agents. @requires and @restrict are the same annotations CAP already has, and the plugin reads them to filter the tool list and the describe output per user and per request, so a model is not told about entities the caller cannot reach — where the OData metadata of the same service lists every exposed entity regardless. The second half annotates a service with @agent from @cap-js/agents, which serves it over A2A with an agent card and a chat preview, runs first against a mocked response and then against SAP AI Core bound with cds bind and a hybrid profile, and reuses the MCP adapter's tools rather than defining new ones.published 2026-08-21
CAP in the age of AI #2 - more on the MCP adapterCAP in the age of AI #2 - more on the MCP adapterWhat the query tool costs in tokens, and the third tool @cap-js/mcp registers. Counted against a model running locally under llama.cpp, the same query is 26 tokens as CQL and 173 as CQN, and the tool definition sent with every system prompt drops from around 5,500 tokens to around 600 — the reason CQL became the default format. The call tool then exposes a service's unbound actions and functions, as one generic tool or, behind a flag, one tool per action with its own description and input schema; a question from the chat about extension points gets the answer that the adapter does the tools, which the panel calls a small subset of the protocol.published 2026-08-14
Add MCP capabilities to a CAP serviceAdd MCP capabilities to a CAP serviceA fifteen-minute walkthrough of turning a plain CAP service into an MCP server: annotate the service with @mcp, install @cap-js/mcp, and it is served alongside OData at /mcp/<path>. The part worth reading it for is what happens next — cds watch writes the endpoint into the local agent's own configuration file, so OpenCode or Claude Code can call the service without anyone editing JSON by hand. It is built on the tiny-sample facet, so there is nothing to prepare, and it shows the protocol traffic rather than only the result. Written while the adapter was in beta, and it says so.published 2026-08-13
CAP in the age of AI #1 - the MCP adapterCAP in the age of AI #1 - the MCP adapterThe episode that opens the series and the first pass over @cap-js/mcp, with four of the people building it on the call. Two of the adapter's tools are worked through: describe, the one an MCP client reaches for first to get the overview of what it may do, and query, which the panel establishes as read-only. It also writes the server entry into a local agent's own configuration file, which episode three comes back to as auto-wiring.published 2026-08-07
CAP in the age of AICAP in the age of AISeven live episodes of Hands-on SAP Dev in which DJ Adams works through CAP's AI features with the people who build them, each one a screen-share against a sample project. The first three are @cap-js/mcp: the @mcp annotation on a service, the describe, query and call tools, CQL as the query format, and what authorisation takes out of the tool list. From episode three the run moves to A2A and @cap-js/agents — human approval of an action, agents.md and skills, session persistence, telemetry and sub-agents — and the last two episodes are vector embeddings in CDS, local on SQLite and native on SAP HANA Cloud.published 2026-08-07
Avoid design time CAP server restarts when maintaining local data filesAvoid design time CAP server restarts when maintaining local data filescds watch restarting on every file change is the feature; this is the case where it is not. Editing a CSV seed file mid-edit restarts the server against half-finished data, and the post is about suppressing that without giving up the watch loop. A small friction most people work around silently rather than fix.published 2024-04-26
Avoid design time CAP server restarts when maintaining local data files
Local development changed in @sap/cds-dk 7.9.1, 2024-05-02. Affects Runnable code.
CAP, CORS and custom headersCAP, CORS and custom headersWhat CAP itself does about CORS, and where it stops. The starting point is a colleague's request and a deliberate constraint: @sap/approuter has full CORS support, but the author wanted to know what the CAP server offers on its own and how to extend it. Ends up covering preflight requests and custom servers, which is the mechanism a frontend hosted outside BTP actually runs into.published 2024-04-11
ISO content for common CAP typesISO content for common CAP typesThe npm package that supplies ISO-standard content — countries, languages, currencies, timezones — for CAP's common types, and how it works underneath. The author flags the length and the reason for it up front, having followed the mechanism further than the question required, which is what makes it worth reading rather than a package announcement.published 2024-03-14
ISO content for common CAP types
Seed data changed in @sap/cds-dk 7.9.1, 2024-05-02. Affects Runnable code.
CAP is important because it's not importantCAP is important because it's not importantAn essay rather than a technique: what CAP actually is, what it gives you, and the case for treating it as foundational precisely because it is not the interesting part of an application. Written in 2019, when that argument still had to be made, and the title is the argument. Also recorded as a Tech Aloud podcast episode and a CodeTalk, both linked from the post.published 2019-11-06
Set up VS Code on Chrome OS for local Application Programming Model developmentSet up VS Code on Chrome OS for local Application Programming Model developmentA CAP development environment on a Chromebook, written from preference rather than constraint — the author sets out why Chrome OS is his primary machine before showing the setup. Carries its own updates section noting what has changed since, which for a 2018 post about an operating system is most of it. The interest now is that local CAP development was portable this early.published 2018-10-16
Set up VS Code on Chrome OS for local Application Programming Model development
Local development has changed twice since this was published, most recently in @sap/cds-dk 7.9.1, 2024-05-02. Affects Runnable code.
SAP Cloud Application Programming Model (CAP) - start hereSAP Cloud Application Programming Model (CAP) - start hereThe orientation post for CAP, published in 2018 and revised in 2020 and again in 2021 with help credited to Iwona Hahn — which is the unusual part: a starting-point index that was maintained rather than left to rot, and says so at the top. Read as the shape of what a newcomer was pointed at, and as a marker of how much of that changed inside three years.published 2018-10-10
CAP Node.js Expert Session #6 - The MCP AdapterCAP Node.js Expert Session #6 - The MCP AdapterDaniel Schlachter and DJ Adams add @cap-js/mcp to a bookshop service, inspect its describe, query and action tools, and query the catalogue through an AI agent. The session distinguishes this runtime adapter from the development-time MCP server and demonstrates automatic registration of the running service with a local agent. The recording describes the adapter as beta in July 2026, with read-only queries and writes through unbound actions.
Examine the details of the Model Context Protocol on startupExamine the details of the Model Context Protocol on startupWhat the MCP adapter actually does when a CAP server boots, watched rather than described — the companion to the tutorial that switches it on.
Define, generate, deploy: AI-driven spec-first TerraformDefine, generate, deploy: AI-driven spec-first TerraformAccount provisioning written as a spec first: the abstract has participants write a structured description of a BTP account, its subaccounts, entitlements, governance, best practices and more, and an AI turns it into Terraform scripts that build it. The abstract does not name the Terraform provider the scripts use, the spec format or the AI behind the generation. A hands-on TechEd 2026 session (Wednesday 28 October, Berlin), presented by Christian Lechner, DJ Adams, Piotr Tesny and Vipin VijayKumar, written here from SAP's abstract; the recording is not yet published.
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- explains → applies_to on 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 Community · cap-tag.
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