Question

I have several database access methods that are wrapped in a try/catch block:

function GetAll() {
    try {
        entityLoad("Book");
    }
    catch (any e) {
        throw (type="CustomException", message="Error accessing database, could not read");
    }
}

function Save(Book book) {
    try {
        entitySave(book);
    }
    catch (any e) {
        throw (type="CustomException", message="Error accessing database, could not save);
    }
}

As you can see, the try/catch block is repeated several times, where the only thing that varies is the message. Is it possible to create a delegate in ColdFusion so that I can do something like this instead (using a C# lambda to represent an anonymous delegate)?:

function GetAll() {
    DatabaseOperation(() => entityLoad("Book"), "could not read");
}

function Save(Book book) {
    DatabaseOperation(() => entitySave(book), "could not save");
}

function DatabaseOperation(delegate action, string error) {
    try {
        action.invoke();
    }
    catch (any e) {
        var message = "Error accessing database, " & error;
        throw (type="CustomException", message=message);
    }
}

Answer 1

Based on your example, not with CF9.

Closures are coming in CF10 which will probably allow you to do something like:

function GetAll() {
    DatabaseOperation( closure(){ entityLoad("Book") } , "could not read");
}

function Save(Book book) {
    DatabaseOperation( closure(){ entitySave(book) } , "could not save");
}

function DatabaseOperation(closure action, string error) {
    try {
        action();
    }
    catch (any e) {
        var message = "Error accessing database, " & error;
        throw (type="CustomException", message=message);
    }
}

(syntax might vary, don’t remember if it was exactly like that)

Alternatively, you could probably use evaluate here, I guess…

function GetAll() {
    DatabaseOperation( 'entityLoad("Book")' , "could not read");
}

function Save(Book book) {
    DatabaseOperation( 'entitySave(book)' , "could not save");
}

function DatabaseOperation(string action, string error) {
    try {
        evaluate(action);
    }
    catch (any e) {
        var message = "Error accessing database, " & error;
        throw (type="CustomException", message=message);
    }
}

Personally I would just remove the try/catch and use onError in Application.cfc – doesn’t seem to be useful to mask the original error and instead throw a more generic one?

Update: two more possible alternatives…

Another option that currently works is to have a public wrapper function, that calls the DatabaseOperation function, passing in the name of a private function that does the actual logic like this:

function GetAll() {
    DatabaseOperation( real_GetAll , Arguments , "could not read");
}
private function real_GetAll() {
    entityLoad("Book")
}

function Save(Book book) {
    DatabaseOperation( real_Save , Arguments , "could not save");
}
private function real_Save(Book book) {
    entitySave(book)
}

function DatabaseOperation(any action, struct args , string error) {
    try {
        action( argumentcollection=args )
    }
    catch (any e) {
        var message = "Error accessing database, " & error;
        throw (type="CustomException", message=message);
    }
}

If you don’t like the idea of defining functions twice, but don’t mind obscuring the API, you could set the methods to private then use onMissingMethod:

private function GetAll()
{
    entityLoad("Book")
}

private function Save(Book book)
{
    entitySave(book)
}

function onMissingMethod( string MethodName , struct MethodArgs )
{
    if ( NOT StructKeyExists(Variables,Arguments.MethodName) )
    {
        throw("The method #Arguments.MethodName# was not found");
    }

    try
    {
        var Meth = Variables[Arguments.MethodName];
        Meth( ArgumentCollection=Arguments.MethodArgs );
    }
    catch(any e)
    {
        var message = "Error accessing database, ";

        switch(MethodName)
        {
            case "GetAll":
                message &= "could not read";
            break;
            case "Save":
                message &= "could not save";
            break;
        }

        throw (type="CustomException,message=message);
    }
}