c# - 您如何保存对 NewExpression 的引用？

Question

我有这个代码:

public static Func<IDataReader, T> CreateBinder<T>() {

    NewExpression dataTransferObject = Expression.New(typeof(T).GetConstructor(Type.EmptyTypes)); 
    ParameterExpression dataReader = Expression.Parameter(typeof(IDataReader), "reader");

    IEnumerable<Expression> columnAssignments = typeof(T).GetProperties().Select(property => {
        MethodCallExpression columnData = Expression.Call(dataReader, dataReaderIndexer, new[] { Expression.Constant(property.Name) });
        MethodCallExpression setter = Expression.Call(dataTransferObject, property.SetMethod, new[] { Expression.Convert( columnData, property.PropertyType ) });

        return setter;
    });

    columnAssignments = columnAssignments.Concat(new Expression[] { dataTransferObject });
    BlockExpression assignmentBlock = Expression.Block(columnAssignments);

    Func<IDataReader, T> binder = Expression.Lambda<Func<IDataReader, T>>(assignmentBlock, new[] { dataReader }).Compile();

    return binder;
}

哪个长话短说将数据库行上的属性绑定(bind)到 <T> .问题是当我想使用/返回 dataTransferObject ，它每次都实例化一个新副本。如何在不重新创建对象的情况下只获取引用？

Answer 1

您只需将 NewExpression 分配给一个变量，然后使用该变量代替 NewExpression。

var dataTransferObject = Expression.Variable(typeof(T), "dto");
var assignment = Expression.Assign(
                     dataTransferObject,
                     Expression.New(typeof(T).GetConstructor(Type.EmptyTypes)));

(将这些表达式添加到 BlockExpression)