Central class for calling static methods in Data Access Layer

Question

Much like the Factory pattern I am looking for a good way to call the desired Data Access methods through a central class. Unfortunately, my DAL classes are static (as I need them to cache records) so I cannot use the Factory pattern. I don't want to convert them into Singletons either unless I see solid benefits in doing so.

In the following code Part is related to Car and Boat via a junction object, and Part has related child objects that need to be returned. This is why some of the methods return Maps:

public class CarDataAccess
{
    public static Car__c[] queryCars(Id[] carIds) { ... }
    public static Car__c[] queryCars(String[] uniqueIds) { ... }
    public static Map<Car__c, Part__c[]> queryAllCars(Boolean activeOnly) { ... }
}

public class BoatDataAccess
{
    public static Boat__c[] queryBoats(Id[] boatIds) { ... }
    public static Boat__c[] queryBoats(String[] uniqueIds) { ... }
    public static Map<Boat__c, Part__c[]> queryAllBoats(Boolean activeOnly) { ... }
}

/*  The Part object has no Unique Id or Active field  */
public class PartDataAccess
{
    public static Part__c[] queryParts(Id[] partIds) { ... }
    public static Part__c[] queryAllParts() { ... }
}

What I currently have is something like this:

public class ObjectDataAccess
{
    public static SObject[] queryObjects(ObjectTypeEnum typ, Id[] ids)
    {
        if (typ == ObjectTypeEnum.CAR) ...
        else if (typ == ObjectTypeEnum.BOAT) ...
        else if (typ == ObjectTypeEnum.PART) ...
        else throw error;
    }

    public static SObject[] queryObjects(ObjectTypeEnum typ, String[] uniqeIds)
    {
        if (typ == ObjectTypeEnum.CAR) ...
        else if (typ == ObjectTypeEnum.BOAT) ...
        else throw error;
    }

    public static SObject[] queryAllObjects(...)
    {
        // NO CLUE!
    }
}

To me this doesn't look right at all. First, this is more of a Util class than anything else! Second, as you can see I have no idea how to handle the different input/output types for the selectAllObjects method.

All ideas for a proper implementation of this problem are welcome.

Answer 1

You might look at how the Selector library does it. Or just use that library; why reinvent the wheel? It allows you to do things like:

// In Service Layer
public static Select.Filter isAccountTask()
{
    return Select.Field.startsWith(Task.WhatId, SObjectType.Account.getKeyPrefix());
}

// In Handler Layer
List<Task> accountTasks = TaskService.isAccountTask().filter(newRecords);

In this case, it seems like you might wish to filter a generic List<SObject> to get the records of a specific type? You might want something like:

public Select.Filter isSObjectType(SObjectType schemaType)
{
    return Select.Field.startsWith('Id', schemaType.getDescribe().getKeyPrefix());
}