Database Lookup mediation primitive
Use the Database Lookup mediation primitive to modify a message, using information from a database.
Introduction
The Database Lookup mediation primitive can add to, or change, messages. It does this using information from a user-supplied database.
You configure the Database Lookup mediation primitive by specifying the database, database table, primary key column, and database column from which to get information. You must also specify where, in the input message, to find the value that is used as the database key.
The Database Lookup mediation primitive has one input terminal (in), two output terminals (out and keyNotFound), and a fail terminal (fail). The in terminal is wired to accept a message and the other terminals are wired to propagate a message. The out terminal is used if the key is located both in the message and the database. In this case, the information obtained from the database is stored in the message and the updated message is propagated. The keyNotFound terminal is used if the key is found in the message, but not in the database. In this case, the original message is propagated unchanged. If an exception occurs during the processing of the input message, the fail terminal propagates the original message, together with any exception information.
Details
Given a database key, the Database Lookup mediation primitive looks up values in a database and stores them as elements in the message.
The information obtained from the database might need converting before it can be stored in the message; you can specify the information type using the Type property. At run time, if the information obtained from the database cannot be converted to the type expected by the message, an exception occurs.
If a message element already exists in the message, the old value is overwritten with the new value.
Usage
You can use the Database Lookup mediation primitive to ensure information in a message is up-to-date.
You can use the Database Lookup mediation primitive to add information to a message, using a key contained in a message. For example, the key could be an account number.
It is often useful to combine the Database Lookup mediation primitive with other mediation primitives. For example, you might use a Mapping mediation primitive to manipulate data, before or after the Database Lookup is invoked.