Question

考虑以下代码，该代码针对EF生成的数据上下文进行调用：

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

如果我更改部门关系的名称，那么此代码将开始抛出运行时错误。那么有没有办法以安全的方式调用.Include（）方法，所以我得到编译时检查所引用的所有关系？

Answer 1

我在Entity Framework 5中使用了以下内容。关键是要包含System.Data.Entity

using System.Data.Entity;

context.Customer
    .Include(c => c.Address)

Answer 2

将moi_meme的想法更进一步，我的同事开发了以下适用于所有情况的解决方案。他介绍了一种新方法Includes()，用于处理一对多和多对多关系。它允许你写这个：

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

这样：

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

所有功劳归于https://stackoverflow.com/users/70427/bojan-resnik，所以如果你喜欢这个解决方案，请给他一些爱。

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);
        }
    }
}

Answer 3

我对ObjectQuery做了一点扩展，就像这样

public static ObjectQuery<TEntity> Include<TEntity, TProperty>(this ObjectQuery<TEntity> query, Expression<Func<TEntity, TProperty>> expression) where TEntity : class
{
    string name = expression.GetPropertyName();
    return query.Include(name);
}

也需要

public static class ExpressionExtensions
{
    public static string GetPropertyName<TObject, TProperty>(this Expression<Func<TObject, TProperty>> expression) where TObject : class
    {
        if (expression.Body.NodeType == ExpressionType.Call)
        {
            MethodCallExpression methodCallExpression = (MethodCallExpression)expression.Body;
            string name = ExpressionExtensions.GetPropertyName(methodCallExpression);
            return name.Substring(expression.Parameters[0].Name.Length + 1);
        }
        return expression.Body.ToString().Substring(expression.Parameters[0].Name.Length + 1);
    }

    private static string GetPropertyName(MethodCallExpression expression)
    {
        MethodCallExpression methodCallExpression = expression.Object as MethodCallExpression;
        if (methodCallExpression != null)
        {
            return GetPropertyName(methodCallExpression);
        }
        return expression.Object.ToString();
    }
}

你可以做到

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

将在编译时检查。如果我没记错的话，这种方法对于多对多关系不起作用，但它适用于像

这样的东西

var item = context.Employees.Include(e => e.Department.Manager);

祝你好运

Answer 4

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

Answer 5

如果您仍在使用Entity Framework 5之前的版本，那么好消息是从C＃6开始，您现在可以使用var context = new DataContext(); var employees = context.Employees.Include(nameof(Employees.Department));来检索任何类/对象的名称。

所以现在你可以做到

{{1}}

如果你正在使用EF＆gt; 5，然后Xavier's answer is better

实体框架.Include（）与编译时检查？

5 个答案: