Many-To-Many Generic Update Method with Entity Framework 6

问题

I have a generic Update method for Entity Framework in an abstract DatabaseOperations<T,U> class:

public virtual void Update(T updatedObject, int key)
{
    if (updatedObject == null)
    {
        return;
    }

    using (var databaseContext = new U())
    {
        databaseContext.Database.Log = Console.Write; 

        T foundEntity = databaseContext.Set<T>().Find(key);
        databaseContext.Entry(foundEntity).CurrentValues.SetValues(updatedObject);
        databaseContext.SaveChanges();
    }
}

However, this does not handle many-to-many relationships.

This many-to-many update problem can be overcome by overriding the Update method in TrussSetDatabaseOperations : DatabaseOperations<TrussSet, TrussManagementDatabaseContext> to read as follows:

public override void Update(TrussSet updatedTrussSet, int key)
{
    if (updatedTrussSet == null)
    {
        return;
    }

    using (var databaseContext = new TrussManagementDatabaseContext())
    {
        databaseContext.Database.Log = Console.Write;

        TrussSet foundTrussSet = databaseContext.TrussSets.Find(key);
        databaseContext.Entry(foundTrussSet).CurrentValues.SetValues(updatedTrussSet)            

        // Update the many-to-many relationship of TrussSets to Seals
        databaseContext.Entry(foundTrussSet).Collection(trussSet => trussSet.Seals).Load();
        databaseContext.Entry(foundTrussSet).Collection(trussSet => trussSet.Seals).CurrentValue = updatedTrussSet.Seals;

        databaseContext.SaveChanges();
    }
}

However, this overriding would proliferate through all the classes that inherit from DatabaseOperations and have a TrussSet object. Can I somehow inject the added two lines into the generic update method, so that the update method is given the collection properties, loads them, and applies the respective updated collection to that entity? Thanks in advance.

回答1:

Looking at your code, the following comes to mind:

public virtual void Update(T updatedObject, int key, params string[] navigationProperties) {
    if (updatedObject == null) {
        return;
    }

    using (var databaseContext = new U()) {
        databaseContext.Database.Log = Console.Write;

        T foundEntity = databaseContext.Set<T>().Find(key);
        var entry = databaseContext.Entry(foundEntity);
        entry.CurrentValues.SetValues(updatedObject);                
        foreach (var prop in navigationProperties) {
            var collection  = entry.Collection(prop);
            collection.Load();
            collection.CurrentValue = typeof(T).GetProperty(prop).GetValue(updatedObject);
        }
        databaseContext.SaveChanges();
    }
}

You can also use Expressions instead of strings (and then extract property names from those expressions) if you want more type-safety.

Update: here is what I mean by "use Expressions" in this case:

public virtual void Update(T updatedObject, int key, params Expression<Func<T, IEnumerable>>[] navigationProperties) {
    if (updatedObject == null) {
        return;
    }


    using (var databaseContext = new U()) {
        databaseContext.Database.Log = Console.Write;

        T foundEntity = databaseContext.Set<T>().Find(key);
        var entry = databaseContext.Entry(foundEntity);
        entry.CurrentValues.SetValues(updatedObject);
        foreach (var prop in navigationProperties) {
            string memberName;
            var member = prop.Body as MemberExpression;
            if (member != null)
                memberName = member.Member.Name;
            else throw new Exception("One of the navigationProperties is not a member access expression");
            var collection = entry.Collection(memberName);
            collection.Load();
            collection.CurrentValue = typeof (T).GetProperty(memberName).GetValue(updatedObject);
        }
        databaseContext.SaveChanges();
    }
}

来源：https://stackoverflow.com/questions/32830764/many-to-many-generic-update-method-with-entity-framework-6