====== 2.1 OData Basics ======

OData((OData - Open Data Protocol: https://www.odata.org/)) (Open Data Protocol) is a REST((Representational State Transfer: https://en.wikipedia.org/wiki/Representational_state_transfer))-based standard for data queries, developed by OASIS((OASIS Open: https://www.oasis-open.org/)).

===== Why OData? =====

  * Native support in [[.:anwender:excel:start|Excel]], [[.:anwender:powerbi:start|Power BI]], [[.:anwender:access:start|Access]]
  * Standardized query syntax((OData Query Options: https://docs.oasis-open.org/odata/odata/v4.01/odata-v4.01-part2-url-conventions.html))
  * Automatic metadata (schema) in CSDL((Common Schema Definition Language: https://docs.oasis-open.org/odata/odata-csdl-json/v4.01/odata-csdl-json-v4.01.html)) format

===== OData Version =====

The Data Gateway supports **OData v4.01**((OData Version 4.01 Specification: https://docs.oasis-open.org/odata/odata/v4.01/odata-v4.01-part1-protocol.html)).

===== Service Document =====

<code>
GET /odata/demo
</code>

Lists all available Entity Sets (tables/views).

===== Metadata =====

<code>
GET /odata/demo/$metadata
</code>

Returns the schema in EDMX((Entity Data Model XML: https://docs.oasis-open.org/odata/odata-csdl-xml/v4.01/odata-csdl-xml-v4.01.html)) format.

===== Query Entity Set =====

<code>
GET /odata/demo/Customers
GET /odata/demo/Customers?$top=10
GET /odata/demo/Customers?$filter=Country eq 'Germany'
</code>

===== Query Options =====

^ Option ^ Description ^ Example ^
| $filter | Filter results | $filter=Price gt 100 |
| $select | Select columns | $select=Name,Price |
| $orderby | Sort results | $orderby=Name desc |
| $top | Limit count | $top=10 |
| $skip | Skip entries | $skip=20 |
| $count | Count results | $count=true |
| $expand | Load relationships | $expand=Orders |

===== Further Reading =====

  * [[.:entwickler:odata:filter|Filter Syntax]] for complex queries
  * [[.:entwickler:odata:paging|Paging]] for large datasets

===== Sources =====

  * [[https://www.odata.org/|OData.org - Official Website]]
  * [[https://docs.oasis-open.org/odata/odata/v4.01/odata-v4.01-part1-protocol.html|OData v4.01 Specification (OASIS)]]
  * [[https://docs.oasis-open.org/odata/odata/v4.01/odata-v4.01-part2-url-conventions.html|OData URL Conventions]]