Odata

---
name: odata
description: "OData 4.x covering Entity Data Model, system query options ($filter, $select, $expand, $orderby, $apply), CSDL metadata, batch requests, functions/actions, and Microsoft/SAP ecosystem integration. Use for \"OData\", \"$filter\", \"$select\", \"$expand\", \"$orderby\", \"$apply\", \"$count\", \"$search\", \"$batch\", \"EDM\", \"CSDL\", \"$metadata\", \"OData query\", \"lambda operator\", \"any\", \"all\", \"navigation property\", \"deep insert\", \"Power BI OData\", \"SAP OData\", \"OData action\", \"OData function\"."
license: MIT
---

# OData 4.x

This skill covers OData (Open Data Protocol), the OASIS standard for RESTful data services. Current versions: OData 4.0 (2014), 4.01 (2020), 4.02 (committee draft 2024). It has deep knowledge of:

- Entity Data Model (EDM): entity types, complex types, navigation properties, inheritance
- System query options: `$filter`, `$select`, `$expand`, `$orderby`, `$top`, `$skip`, `$count`, `$search`, `$apply`, `$format`
- CSDL metadata document (`$metadata`) and service document
- CRUD operations, deep insert, upsert
- Functions (side-effect-free) and Actions (side effects)
- Batch requests (`$batch` -- multipart and JSON formats)
- Lambda operators (`any`, `all`) for collection filtering
- Data aggregation via `$apply` (groupby, aggregate, filter, compute)
- Microsoft ecosystem: Azure, SharePoint, Dynamics 365, Power Platform
- SAP ecosystem: SAP Gateway, S/4HANA OData APIs

## How to Approach Tasks

1. **Classify** the request:
   - **Data model / schema design** -- Load `references/architecture.md` for EDM, CSDL, entity/complex types, navigation properties
   - **Query design / best practices** -- Load `references/best-practices.md` for query options, aggregation, batch, performance
   - **Troubleshooting / diagnostics** -- Load `references/diagnostics.md` for query errors, metadata issues, batch failures
   - **Cross-protocol comparison** -- Read the `overview` skill

2. **Gather context** -- OData version (4.0 vs 4.01), server framework (.NET, SAP, Java), consumer tooling (Power BI, Excel, custom client)

3. **Analyze** -- Apply OData-specific reasoning: query option composition, metadata-driven client generation, aggregation pipeline design.

4. **Recommend** -- Provide URL examples, CSDL snippets, and server configuration.

## Core Architecture

### Entity Data Model

**Entity Type**: structured type with a key (like a database table row). **Complex Type**: structured type without a key (embedded value). **Entity Set**: collection of entities (addressable via URL). **Singleton**: single entity instance.

### System Query Options

| Option | Purpose | Example |
|---|---|---|
| `$filter` | Filter by boolean expression | `$filter=Price gt 20` |
| `$select` | Return only specified properties | `$select=Name,Price` |
| `$expand` | Include related entities inline | `$expand=Items($select=Name)` |
| `$orderby` | Sort results | `$orderby=Price desc` |
| `$top` / `$skip` | Pagination | `$top=10&$skip=20` |
| `$count` | Include total count | `$count=true` |
| `$search` | Full-text search | `$search=widget` |
| `$apply` | Aggregation pipeline | `$apply=groupby((Category),aggregate($count as Count))` |

### Lambda Operators

`any` (at least one element matches) and `all` (every element matches):
```
$filter=Tags/any(t: contains(t, 'sale'))
$filter=Reviews/all(r: r/Rating ge 4)
```

### Metadata

`$metadata` endpoint exposes full schema as CSDL. Consumer tooling generates clients from this.

## Anti-Patterns

1. **No `$select` on large entity types** -- Returning all 50 columns when client needs 3. Always encourage `$select`.
2. **Unbounded `$expand`** -- `$expand=*` without limits can generate enormous responses. Restrict expansion depth.
3. **`$skip` on large datasets** -- Offset pagination degrades on large tables. Use server-driven paging with `@odata.nextLink`.
4. **Ignoring `@odata.nextLink`** -- Server-side paging is mandatory for large result sets. Clients must follow `@odata.nextLink`.
5. **Batch without changesets for atomic operations** -- Related modifications must be in a changeset for atomicity.
6. **Actions when Functions suffice** -- Side-effect-free operations should be Functions (GET), not Actions (POST).
7. **Open types without validation** -- Open types accept any property. Validate dynamic properties server-side.

## Reference Files

- `references/architecture.md` -- EDM, CSDL, entity/complex types, navigation properties, inheritance, URL structure, metadata
- `references/best-practices.md` -- Query composition, $apply aggregation, batch requests, functions/actions, deep insert, performance, versioning
- `references/diagnostics.md` -- Query syntax errors, $filter issues, $expand failures, batch errors, metadata problems, performance

## Cross-References

- `overview` skill -- OData vs REST/GraphQL comparisons
- `rest` skill -- REST design principles (OData builds on REST)