c# - 林奇 : Dynamic select

Question

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; }

}

如何动态选择指定列？像这样:

  var list = new List<Data>();

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

这是唯一的解决方案吗=> Dynamic LINQ ?
选定的字段在编译时是未知的。它们将在运行时指定

Answer 1

您可以通过动态创建传递给 Select:

的 lambda 来实现这一点

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();
}

然后你可以像这样使用它:

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