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Saturday, April 9, 2011

Component Field COLUMN_LIST in Talend Open Studio

If your Talend Open Studio custom component needs to select from a list of columns in an input or output schema, use the COLUMN_LIST field type.  By default, this will display fields from the FLOW schema.  To select columns from other schemas, define a different CONNECTOR and use the CONTEXT attribute.

The COLUMN_LIST field type is a PARAMETER that enables the user to select from a list of columns of a schema.  For example, this screenshot shows two COLUMN_LIST fields "Reason code column" and "Reason message column".  Both of these COLUMN_LISTS are based on a schema associated with the REJECT connector.

FIELD=COLUMN_LIST in Component View
XML Configuration

A COLUMN_LIST parameter is created using the FIELD, NAME, and NUM_ROWS attributes.  "FIELD" is set to COLUMN_LIST.  "NAME" is a unique name used in the JET code.  "NUM_ROWS" is the display line of the COLUMN_LIST.  This particular example also uses a GROUP attribute to relate the two COLUMN_LIST parameters under "Reject fields".

 Linking Schemas

 The above configuration of the COLUMN_LIST parameter contains a CONTEXT attribute.  This is the name of a input or output schema associated with a CONNECTOR.  For example, there is a CONNECTOR named "REJECT".  This connector is configured with a parameter named "SCHEMA_REJECT" which also refers to the REJECT context.

 The column list value is retrieved the ElementParameterParser.getValue() call.

Properties Note
The column list will accept .NAME properties.  In 4.1.0, COLUMN_LIST is a little different in that a presentable label is displayed if none is provided.  "Column list" is displayed, rather than "!!!COLUMN_LIST.NAME!!" as in other cases.

COLUMN_LIST will let the user select a schema column in Component View.  This selected column is available in the JET or Java code associated with the component.  Off-the-shelf, COLUMN_LIST displays FLOW columns.  With additional CONNECTORS, COLUMN_LIST can be pointed to other schemas.

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