在运行时解析属性。 C＃

Question

I have some class which have some code

public IEnumerable<TypeOne> TypeOne
    {
        get
        {
            if (db != null)
            {
                var col = db.Select<TypeOne>();
                if (col.Count > 0) return col;
            }
            return db2.TypeOne;
        }
    }
    public IEnumerable<TypeTwo> TypeTwo
    {
        get
        {
            if (db != null)
            {
                var col = db.Select<TypeTwo>();
                if (col.Count > 0) return col;
            }
            return db2.TypeTwo;
        }
    }

So as You can see there is a lot of duplicated Code and there are same property name and item type of enumerable. I want to call some property of object like "obj.MyProp". And MyProp must be resolved at runtime with some generic or non-generic method. Is it possible?

Answer 1

Slightly incomplete answer but you'll get the general idea:

This is a scenario where you want generics.

public IEnumerable<t> TypeSomething
{
    get
    {
        if (db != null)
        {
            t col = db.Select<t>();
            if (col.Count > 0) return col;
        }
        return GetDB<t>();
    }
}

You'd need to implement GetDB() to return the appropriate db for any given type, but that'd be a single switch (or you can use reflection to find it)

Answer 2

You can solve this by using generics:

public IEnumerable<TypeOne> TypeOne
{
    get { return GetTable<TypeOne>(); }
}

public IEnumerable<TypeTwo> TypeTwo
{
    get { return GetTable<TypeTwo>(); }
}

private IEnumerable<T> GetTable<T>()
{
    if (db != null)
    {
        var col = db.Select<T>();
        if (col.Count > 0) return col;
    }

    return db2.Select<T>();    
}

Answer 3

There are a couple of ways to do this. The best is probably a generic method:

public IEnumerable<T> dbSelect<T>() //may need type constraints here
{
    return db != null
           ? db.Select<T>()
           : null;
}
public IEnumerable<TypeOne> TypeOne
{
    get { return dbSelect<TypeOne> ?? db2.TypeOne; }
}
public IEnumerable<TypeTwo> TypeTwo
{
    get { return dbSelect<TypeTwo>() ?? db2.TypeTwo; }
}

If your db2 object has a generic Select<T> -type method like db does, it's even easier:

public IEnumerable<T> dbSelect<T>()
{
    return db != null
           ? db.Select<T>()
           : db2.Select<T>(); //or db2.GetEntities<T>() or db2.OfType<T> or whatever
}

//Later, in your main code...
var x = dbSelect<TypeOne>();
var y = dbSelect<TypeTwo>();

This will be type safe, considerably faster than reflection, and will work with Intellisense.