# MemDataSource

## Overview

Servoy allows the creation of **In-Memory** tables using HSQL, which behave like regular database tables with similar configurations, including column properties and events. These tables can be populated using a *JSDataSet* and the `createDataSource()` function to dynamically define datasources or foundsets at runtime.

If the In-Memory table was predefined in Servoy Developer, there is no need to re-define column and type information during runtime.

## Creating In-Memory Databases

There are two ways to create an In-Memory database:

* Via the [Solution Explorer](https://docs.servoy.com/reference/servoy-developer/solution-explorer), under *Datasources -> In Memory -> Create new data source*. This opens a dialog to specify the datasource name and the [Table Editor](https://docs.servoy.com/reference/servoy-developer/object-editors/table-editor) for table structure definition.
* At runtime, using the [JSDataSet::createDataSource](https://docs.servoy.com/reference/servoycore/dev-api/database-manager/jsdataset#createdatasourcename) function to dynamically define datasources.

## Additional Table Event: onLoad

In-Memory tables have an extra event called **onLoad**, triggered when a form accesses the In-Memory datasource or when `datasource.mem.name.getFoundSet()` is called. This event allows on-demand population of the datasource, but you must still use `createDataSource()` in the **onLoad** method to populate the table.

## Commands Summary

* ***Create in memory datasource*** - Opens the [Table Editor](https://docs.servoy.com/reference/servoy-developer/object-editors/table-editor).
* ***Edit table/view*** - Edits table structure via the [Table Editor](https://docs.servoy.com/reference/servoy-developer/object-editors/table-editor).
* ***Delete In Memory Datasource*** - Deletes the datasource definition.
* ***Rename In Memory Datasource*** - Renames the datasource definition.
* ***Search for references*** - Finds locations within the solution where the datasource is used.

For more details, please refer to the [In-memory Databases](https://docs.servoy.com/guides/develop/application-design/data-modeling/in-memory-databases) section of the **Data modeling** documentation.

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