实体框架.INCLUDE（）与编译时检查？

问题描述

考虑以下code，该呼吁针对EF生成的数据方面：

Consider the following code, which is calling against an EF generated data context:

var context = new DataContext();
var employees = context.Employees.Include("Department");

如果我更改系关系的名字，那么这个code将开始抛出运行时错误。那么，有没有办法来调用一个安全的方式.INCLUDE（）方法，所以我得到的编译时间检查所引用的所有关系？

If I change the name of the Department relationship then this code is going to start throwing a runtime error. So is there any way to call the .Include() method in a safe manner, so I get compile time checking for all the relationships being referenced?

推荐答案

以moi_meme的想法更进了一步，我的同事开发了以下解决方案，它在所有情况下工作。他介绍caled的新方法包括（）处理一个一对多和多对多的一对多关系。它可以让你写这篇文章：

Taking moi_meme's idea a step further, my colleague developed the following solution that works in all cases. He introduced a new method caled Includes() for dealing with one-to-many and many-to-many relationships. It allows you to write this:

context.Customer
    .Include("Address")
    .Include("Orders")
    .Include("Orders.OrderLines")

，如下：

context.Customer
    .Include(c => c.Address)
    .Includes(c => c.Include(customer => customer.Orders)
                    .Include(order => order.OrderLines))

一切归功于http://stackoverflow.com/users/70427/bojan-resnik,所以要多给他一些爱，如果你喜欢的解决方案。

All credit goes to http://stackoverflow.com/users/70427/bojan-resnik, so go give him some love if you like the solution.

public static class ObjectQueryExtensions
{
    public static ObjectQuery<T> Includes<T>(this ObjectQuery<T> query, Action<IncludeObjectQuery<T, T>> action)
    {
        var sb = new StringBuilder();
        var queryBuilder = new IncludeObjectQuery<T, T>(query, sb);
        action(queryBuilder);
        return queryBuilder.Query;
    }

    public static ObjectQuery<TEntity> Include<TEntity, TProperty>(this ObjectQuery<TEntity> query, Expression<Func<TEntity, TProperty>> expression)
    {
        var sb = new StringBuilder();
        return IncludeAllLevels(expression, sb, query);
    }

    static ObjectQuery<TQuery> IncludeAllLevels<TEntity, TProperty, TQuery>(Expression<Func<TEntity, TProperty>> expression, StringBuilder sb, ObjectQuery<TQuery> query)
    {
        foreach (var name in expression.GetPropertyLevels())
        {
            sb.Append(name);
            query = query.Include(sb.ToString());
            Debug.WriteLine(string.Format("Include(\"{0}\")", sb));
            sb.Append('.');
        }
        return query;
    }

    static IEnumerable<string> GetPropertyLevels<TClass, TProperty>(this Expression<Func<TClass, TProperty>> expression)
    {
        var namesInReverse = new List<string>();

        var unaryExpression = expression as UnaryExpression;
        var body = unaryExpression != null ? unaryExpression.Operand : expression.Body;

        while (body != null)
        {
            var memberExpression = body as MemberExpression;
            if (memberExpression == null)
                break;

            namesInReverse.Add(memberExpression.Member.Name);
            body = memberExpression.Expression;
        }

        namesInReverse.Reverse();
        return namesInReverse;
    }

    public class IncludeObjectQuery<TQuery, T>
    {
        readonly StringBuilder _pathBuilder;
        public ObjectQuery<TQuery> Query { get; private set; }

        public IncludeObjectQuery(ObjectQuery<TQuery> query, StringBuilder builder)
        {
            _pathBuilder = builder;
            Query = query;
        }

        public IncludeObjectQuery<TQuery, U> Include<U>(Expression<Func<T, U>> expression)
        {
            Query = ObjectQueryExtensions.IncludeAllLevels(expression, _pathBuilder, Query);
            return new IncludeObjectQuery<TQuery, U>(Query, _pathBuilder);
        }

        public IncludeObjectQuery<TQuery, U> Include<U>(Expression<Func<T, EntityCollection<U>>> expression) where U : class
        {
            Query = ObjectQueryExtensions.IncludeAllLevels(expression, _pathBuilder, Query);
            return new IncludeObjectQuery<TQuery, U>(Query, _pathBuilder);
        }
    }
}

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