Adobe 38043740 Developing Applications - Page 686

DEVELOPING COLDFUSION 9 APPLICATIONS 681 Flex and AIR Integration in ColdFusion You place the database manipulation functionality directly in the methods in the assembler CFC and create a Value Object CFC, which is a CFC that contains property definitions and related get and set methods. To separate the lower level database functionality from the high-level Flex assembler operations, you create a Data Access Object (DAO) CFC that contains the lower level database functionality. Using this approach, which is the Bean/DAO methodology, requires that you place the fill, get, sync, and count methods in the assembler CFC. The methods in the assembler CFC call methods in the DAO CFC that perform the lower level database functions such as retrieving records. The DAO CFC creates Value Objects, which are CFCs that contain the values. A Value Object is essentially a row in the result set. The LiveCycle Data Management Service recognizes the methods: fill, get, sync, and count. The fill method retrieves records from a database and populates an array with the records. The get method retrieves a specific record. The sync method lets you keep track of synchronization conflicts by accepting a change list, which is an array of change objects. The count method returns a number that indicates how many records are in a result set. To perform any of these database tasks, the Flex application calls the appropriate fill, get, sync, or count method in the assembler CFC. You can also use a fillContains method, which checks whether to update the results of a fill. For more information, see "Managing fills" on page 683. Creating the fill method The fill method retrieves records from a database and populates an array with the records. If you use the Bean/DAO methodology, you create the lower level read method separately in the DAO CFC. The fill method returns the results of a read operation. In the fill method, you create an array to hold the results of the read, and then return the results of the read operation. The essential elements of a fill method appear as follows: You can return a Value Object CFC, a query, or an array of CFML structures. Using a query instead of a Value Object CFC may improve performance. However, ColdFusion cannot handle nested results sets when you use a query. For example, if one of the CFC properties you are returning from the fill method was populated with another complex type such as another CFC type, ColdFusion cannot automatically convert a column in the query to an object with a custom type. In this case, you return an array of CFCs, and the fill method or the read method in the DAO CFC constructs the correct object. You can use structures wherever you currently create a ColdFusion component in the Assembler. However, you still receive CFC Value Objects from Flex. For example, the Change Objects that you receive in the sync method contain CFCs, assuming that you have a remote alias defined in the ActionScript type. You can create Value Object CFCs in the get method. However, using the structure functionality, you can create and return a structure instead of a CFC, because the structures are translated in the same way as CFCs. You can also return an array of structures from the fill method instead of an array of CFCs, for example, if you have to do processing on your data and working with CFCs isn't fast enough. Generally, structures are faster than CFCs. You also use structures when a member of the result object is a complex object. In this case, you create another structure as the value of that key and provide the __type__ key for it. You specify the returntype of the fill method as a Value Object CFC, a query, or an array: 1 Value Object: 2 Query: Last updated 1/20/2012