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12.25. OData Translator
12.25.1. OData Translator
The OData translator exposes the OData V2 and V3 data sources. This translator implements a simple connection for web services in the same way as the Web Services translator.
The OData translator is implemented by the
org.teiid.translator.odata.ODataExecutionFactory class and known by the translator type name odata.
Note
Open Data Protocol (OData) is a Web protocol for querying and updating data that provides a way to unlock your data and free it from silos that exist in applications today. OData does this by applying and building upon Web technologies such as HTTP, Atom Publishing Protocol (AtomPub) and JSON to provide access to information from a variety of applications, services, and stores. OData is being used to expose and access information from a variety of sources including, but not limited to, relational databases, file systems, content management systems and traditional Web sites.
Using this specification from OASIS group, and with the help from framework OData4J, JBoss Data Virtualization maps OData entities into relational schema. JBoss Data Virtualization supports reading of CSDL (Conceptual Schema Definition Language) from the OData endpoint provided and converts the OData schema into relational schema. The below table shows the mapping selections in OData Translator from CSDL document.
|
OData
|
Mapped to Relational Entity
|
|---|---|
|
EntitySet
|
Table
|
|
FunctionImport
|
Procedure
|
|
AssociationSet
|
Foreign Keys on the Table*
|
|
ComplexType
|
ignored**
|
* A Many to Many association will result in a link table that can not be selected from, but can be used for join purposes.
** When used in Functions, an implicit table is exposed. When used to define a embedded table, all the columns will be in-lined.
All CRUD operations will be appropriately mapped to the resulting entity based on the SQL submitted to the OData translator.
Note
The resource adapter for this translator is provided by configuring the
webservice data source in the JBoss EAP instance. See the Red Hat JBoss Data Virtualization Administration and Configuration Guide for more configuration information.
Using this specification from OASIS group, with the help from the Olingo framework, Teiid maps OData V4 CSDL (Conceptual Schema Definition Language) document from the OData endpoint provided and converts the OData metadata into Teiid's relational schema. The below table shows the mapping selections in OData V4 Translator from CSDL document
12.25.2. OData Translator: Execution Properties
|
Name
|
Description
|
Default
|
|---|---|---|
|
DatabaseTimeZone
|
The time zone of the database. Used when fetching date, time, or timestamp values
|
The system default time zone
|
12.25.3. OData Translator: Importer Properties
|
Name
|
Description
|
Default
|
|---|---|---|
|
schemaNamespace
|
Namespace of the schema to import
|
null
|
|
entityContainer
|
Entity Container Name to import
|
default container
|
Example importer settings to only import tables and views from NetflixCatalog:
<property name="importer.schemaNamespace" value="System.Data.Objects"/> <property name="importer.schemaPattern" value="NetflixCatalog"/>
12.25.4. OData Translator: Usage
Usage of an OData source is similar to a JDBC translator. The metadata import is supported through the translator, once the metadata is imported from source system and exposed in relational terms, then this source can be queried as if the EntitySets and Function Imports were local to the JBoss Data Virtualization system.
| Property | Description | Default |
|---|---|---|
| DatabaseTimeZone |
The time zone of the database. Used when fetchings date, time, or timestamp values
|
The system default time zone
|
| SupportsOdataCount |
Supports $count
|
True
|
| SupportsOdataFilter |
Supports $filter
|
True
|
| SupportsOdataOrderBy |
Supports $orderby
|
true
|
| SupportsOdataSkip |
Supports $skip
|
True
|
| SupportsOdataTop |
Supports $top
|
True
|
| Property | Description | Default |
|---|---|---|
| schemaNamespace |
Namespace of the schema to import
|
Null
|
| entityContainer |
Entity Container Name to import
|
Default container
|
Here are some importer settings to import tables and views only from NetflixCatalog:
<property name="importer.schemaNamespace" value="System.Data.Objects"/> <property name="importer.schemaPattern" value="NetflixCatalog"/>
Note
Sometimes it's possible that the odata server you are querying does not fully implement all OData specification features. If your OData implementation does not support a certain feature, then turn off the corresponding capability using "execution Properties", so that Teiid will not pushdown invalid queries to the translator. For example, to turn off $filter you add following to your vdb.xml then use "odata-override" as the translator name on your source model:
<translator name="odata-override" type="odata"> <property name="SupportsOdataFilter" value="false"/> </translator>
Note
Native or direct query execution is not supported through OData translator. However, user can use Web Services Translator's invokehttp method directly to issue a Rest based call and parse results using SQLXML.
Note
Teiid can not only consume OData based data sources, but it can expose any data source as an Odata based webservice. For more information see OData Support.
