CODEWITHSUNDEEP
c#generics
Eric Herlitz
Eric Herlitz

Reputation: 26267

Get Key and Value types from dictionary in generic method

Id like to be able to work with Dictionaries in generic methods. What Im looking for is a way to get the Type from Key and Value of the dictionary sent to the generic extension method LoadProperty.

This is what I've done so far.

I call the method as an extension

entityObject.LoadProperty<Dictionary<string, int>>("CartonThreshold")
//entityObject.LoadProperty<Dictionary<string, double>>("CartonThreshold")

// ... 

public static T LoadProperty<T>(this EntityObject entity, string name) where T : new()
{
    EntityObjectProperty prop = entity.Properties.Single(x => x.Name.Equals(name));

    // If request dictionary
    if (typeof(T).GetInterface(typeof(IDictionary<,>).Name) != null || typeof(T).Name.Contains("IDictionary"))
    {
        var dictionaryInstance = (IDictionary)new T();

        // Just for testing
        var a = dictionaryInstance.Keys.GetType().Name;
        var b = dictionaryInstance.Values.GetType().Name;

        var key = (T) Convert.ChangeType(prop.Name, typeof (T));
        var value = (T) Convert.ChangeType(prop.Value, typeof (T));
        dictionaryInstance.Add(key, value);
        return (T) dictionaryInstance;
    }

    // default
    return (T)Convert.ChangeType(prop.Value, typeof(T));
}

The goal is to return a correctly typed dictionary

Upvotes: 1

Views: 4734

Answers (4)

Paolo Tedesco
Paolo Tedesco

Reputation: 57202

If I understood your question correctly, what you would like to do is define your method like this:

public static T LoadProperty<T,TKey,TValue>(this EntityObject entity, string name) 
    where T : IDictionary<TKey,TValue>, new() {
    EntityObjectProperty prop = entity.Properties.Single(x => x.Name.Equals(name));
    T t = new T();
    t.Add((TKey)prop.Name, TValue(prop.Value));
    return t;
}

Then call it with

Dictionary<string,int> property = entityObject.LoadProperty<Dictionary<string,int>, string, int>("test");

The bad thing is that you have to specify all the generic parameters each time...
If it's ok for your concrete case, it would be much simpler like this:

public static IDictionary<TKey,TValue> LoadProperty<TKey,TValue>(this EntityObject entity, string name) {
    EntityObjectProperty prop = entity.Properties.Single(x => x.Name.Equals(name));
    var dict = new Dictionary<TKey,TValue>();
    dict.Add((TKey)prop.Name, TValue(prop.Value));
    return dict;
}

EDIT: after your clarification, what about telling the two cases apart by the number of generic arguments?

public static IDictionary<TKey,TValue> LoadProperty<TKey,TValue>(this EntityObject entity, string name) {
    var d = new Dictionary<TKey,TValue>();
    // add value from EntityObject 
    return t;
}

public static TValue LoadProperty<TValue>(this EntityObject entity, string name) {
    TValue ret;
    // get value from EntityObject 
    return ret;
}

Upvotes: 0

phipsgabler
phipsgabler

Reputation: 20950

To get it working with almost anything, you could pass a function to create whatever return type you want:

public static T LoadProperty<TKey,TValue,T>(this EntityObject entity, string name,  Func<TKey,TValue,T> createWhatever) 
{
    EntityObjectProperty prop = entity.Properties.Single(x => x.Name.Equals(name));
    return createWhatever((TKey)prop.Name, (TValue)prop.Value);
}

This would be a bit more verbose at the calling, though.

Upvotes: 0

Eric Herlitz
Eric Herlitz

Reputation: 26267

What I was looking for was the GetGenericArguments() extension of GetType()

The method below will return what I need.

public static T LoadProperty<T>(this EntityObject entity, string name) where T : new()
{
    EntityObjectProperty prop = entity.Properties.Single(x => x.Name.Equals(name));

    try
    {
        // If request dictionary
        if (typeof(T).GetInterface(typeof(IDictionary<,>).Name) != null || typeof(T).Name.Contains("IDictionary"))
        {
            var dictionaryInstance = (IDictionary)new T();

            var typing = dictionaryInstance.GetType().GetGenericArguments();
            Type keyType = typing[0];
            Type valueType = typing[1];

            // dictionary fallback, set to default of the valuetype if null
            object value = prop.Value != null ? Convert.ChangeType(prop.Value, valueType) : Activator.CreateInstance(valueType);
            var key = Convert.ChangeType(prop.Name, keyType);
            dictionaryInstance.Add(key, value);
            return (T)dictionaryInstance;
        }

        if (prop.Value != null)
        {
            // default
            return (T)Convert.ChangeType(prop.Value, typeof(T));
        }
    }
    catch { }
    return default(T);
}

This way I can call the method like this

// Will return a typed dictionary with the EntityObjectProperty name as key and the EntityObjectProperty Value as value
entityObject.LoadProperty<Dictionary<string, int>>("CartonThreshold")

// Will return a string of the EntityObjectProperty Value
entityObject.LoadProperty<string>("CartonThreshold")

// Will return an Int of the EntityObjectProperty Value
entityObject.LoadProperty<int>("CartonThreshold")

Upvotes: 1

Ventsyslav Raikov
Ventsyslav Raikov

Reputation: 7192

Why don't you just define your method like this:

public static IDictionary<K, V> LoadProperty<K, V>(this EntityObject entity, string name)

Upvotes: 0

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