c# - LINQ vs context.entity.Where()

Question

这两个块是否完全相同？一个相对于另一个有什么优势吗？

        using (var context = new TRANSITEntities())
        {
            var result = context.Table1.Where(c => c.UserCode == "123");
        }


        using (var context = new TRANSITEntities())
        {
            var result = from c in context.Table1
                         where c.UserCode == "123"
                         select c;
        }

Answer 1

一模一样。

您可以通过查看ToString（）来验证自己

    string query1String, query2String;
    using (var context = new TRANSITEntities())
    {
        var result = context.Table1.Where(c => c.UserCode == "123");
        query1String = result.Expression.ToString();
    }


    using (var context = new TRANSITEntities())
    {
        var result = from c in context.Table1
                     where c.UserCode == "123"
                     select c;
        var query2String = result.Expression.ToString();
    }

    Assert.AreEqual(query1String, query2String);

还应注意，result实际上不是结果。这是未执行/枚举的IQueryable。这意味着它就像尚未运行（某种）的SQL语句。如果你要做

    var t1 = result.ToArray()
    var t2 = result.ToArray()

那么查询实际上将执行两次。 t1和t2是REAL结果（在内存数组中）...不是result。换句话说，result应该真正被命名为query并且，上面的示例将永远无法工作...因为如果在ToArray块之外的结果上调用using，它将失败。 ..因为一旦上下文被处理，您将无法运行查询：

    using (var context = new TRANSITEntities())
    {
        var result = context.Table1.Where(c => c.UserCode == "123");
    }
    // throws exception:
    var array = result.ToArray();