> For the complete documentation index, see [llms.txt](https://docs.rierino.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rierino.com/devops/pro-code/custom-query-managers.md).

# Custom Query Managers

Custom state managers can be created and added to runners to query new data sources, if needed.

All query managers extend the abstract QueryManager class or one of its subclasses.

```java
public class MyQueryManager extends QueryManager{

  /** 
   * Constructor with provided "alias", event runner which owns the manager
   * as well as all the configurations available to the runner
   */
  public MyQueryManager(String name, EventRunner runner, Map<String, String> config) {
    super(name, runner, config);
  }
  
  /** 
   * Function called during initialization of a query manager, typically
   * used to establish connections.
   */
  @Override
  public void configure() throws HotException {
  }
   
  /** 
   * Function called during termination of a query manager, typically
   * used to close connections with external systems.
   */
  @Override
  public void close() throws IOException {
  }
  
  /**
   * Function called for streaming records from
   * the query manager for a given query definition.
   * Data can be returned in any format preferred by the target
   * system, as convertToJson function is called for the output.
   */
  @Override
  public abstract Stream getRawQueryStream(Query query, InjectionHelper helper) throws HotException{
  }

  /**
   * Function called for translating target system specific records
   * into JsonNode.
   */
   public JsonNode convertToJson(Object object) throws HotException{
   }

}
```

Query managers typically utilize query producers for translating Rierino platform specific query definitions into target system specific language (e.g. SQL).  Query producers implement a wide range of abstract functions to provide this support, depending on their type:

* **CommandProducer:** For translating open ended query definitions to target system
* **SimpleProducer:** For translating regular queries with where condition, field selection and joins
* **AggregationProducer:** For translating group by and aggregation queries
* **PipelineProducer:** For translating step by step query pipelines supported by certain systems (e.g. MongoDB)
* **BundleProducer:** For translating bundled queries which submit multiple queries at once, supported by certain systems (e.g. Elasticsearch)


---

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