LINQ：动态选择 [英] LINQ : Dynamic select

问题描述

考虑，我们有这个类：

    public  class Data
{
    public string Field1 { get; set; }
    public string Field2 { get; set; }
    public string Field3 { get; set; }
    public string Field4 { get; set; }
    public string Field5 { get; set; }

}

如何动态地选择指定的列？是这样的：

How do I dynamically select for specify columns ? something like this :

  var list = new List<Data>();

  var result= list.Select("Field1,Field2"); // How ?

这是唯一的解决方案=> Dynamic LINQ ？结果
所选字段不会在编译时已知。他们会在运行时指定

Is this the only solution => Dynamic LINQ ?
Selected fields are not known at compile time. They would be specified at runtime

推荐答案

您可以通过动态创建您传递给拉姆达做选择：

You can do this by dynamically creating the lambda you pass to Select:

Func<Data,Data> CreateNewStatement( string fields )
{
    // input parameter "o"
    var xParameter = Expression.Parameter( typeof( Data ), "o" );

    // new statement "new Data()"
    var xNew = Expression.New( typeof( Data ) );

    // create initializers
    var bindings = fields.Split( ',' ).Select( o => o.Trim() )
        .Select( o => {

            // property "Field1"
            var mi = typeof( Data ).GetProperty( o );

            // original value "o.Field1"
            var xOriginal = Expression.Property( xParameter, mi );

            // set value "Field1 = o.Field1"
            return Expression.Bind( mi, xOriginal );
        }
    );

    // initialization "new Data { Field1 = o.Field1, Field2 = o.Field2 }"
    var xInit = Expression.MemberInit( xNew, bindings );

    // expression "o => new Data { Field1 = o.Field1, Field2 = o.Field2 }"
    var lambda = Expression.Lambda<Func<Data,Data>>( xInit, xParameter );

    // compile to Func<Data, Data>
    return lambda.Compile();
}

然后你可以使用这样的：

Then you can use it like this:

var result = list.Select( CreateNewStatement( "Field1, Field2" ) );

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