C# How to serialize system.linq.expressions?

问题:

I am working on winRT and entity framework (to SQL), the layer that communicates between them is WCF Service. In the entity framework I am using the Repository Pattern and I have the method:

public IQueryable<User> GetBySearch(Expression<Func<User, bool>> search)
{
    return this.Context.Users.Where(search);
}

Everything works fine, but when I add it to WCF

[OperationContract]
IQueryable<User> GetUserBySearch(Expression<Func<User, bool>> search);

and:

public IQueryable<User> GetUserBySearch(Expression<Func<User, bool>> search)
{
    IUser user = new UserRepository();
    return user.GetBySearch(search);
}

But the problem that Expression is not serializable, therefore, WCF can't serialize it. So I thought to inherit from it and make it [Serializable] but the problem that it is a sealed class.

Can someone help me to solve the problem?

回答1:

WCF doesn't play well with Iqueryable and lambdas if your are using Entity Framework. This is a quick and dirty solution, adapt it to your needs.

Change the service contract to

[OperationContract]
IEnumerable<User> GetEventBySearch(UserCriteria search);

Where UserCriteria is a DataContract that contains a property for every search criteria that you need - example:

[DataContract]
public class UserCriteria
{
    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public string Email { get; set; }

    // add a property for each search criteria....
}

Service implementation:

public IEnumerable<User> GetEventBySearch(UserCriteria search)
{
    IUser user = new UserRepository();
    Expression<Func<User, bool>> criteria = BuildExpression(search);

    return user.GetBySearch(criteria).AsEnumerable();
}

private Expression<Func<User, bool>> BuildExpression(UserCriteria search)
{
    // build lambda expression here
}

回答2:

Changeing Your Expression To Func , You Can Use BinaryFormatter Or Other Serializers To Serialize It As You Wish

回答3:

You can use ServicePredicateBuilder to serialize expressions. http://www.codeproject.com/Articles/851187/ServicePredicateBuilder-for-creating-Serializable