用c#构建LINQ动态表达式

我想动态地构建linq表达式，在以下Select语句中使用从DB填充的数据表:

IQueryable iq = myDataTable
    .AsEnumerable()
    .AsQueryable()
    .Select(
        d => new {
            Field1 = d.Field<int>(37),
            Field2 = d.Field<string>(0),
            Field3 = d.Field<DateTime>(1)
            }
    );

字段在运行时之前是未知的。我将在运行时获得字段列表("Field1"，"Field2"，"Field3"…)，它们的类型(int, string, datetime…)和它们的索引(37,0,1…)。

有什么方法可以做到这一点吗?

Type type = typeof(DataRow);
MethodInfo mi1 = typeof(DataRowExtensions).GetMethod("Field", new Type[] { typeof(DataRow), typeof(int) });
mi1 = mi1.MakeGenericMethod(type);
List<Expression> list1 = new List<Expression>();
ParameterExpression datarow1 = Expression.Parameter(type, "datarow");
ConstantExpression constant1 = Expression.Constant(37, typeof(int));
list1.Add(datarow1);
list1.Add(constant1);
ReadOnlyCollection<Expression> collection1 = new ReadOnlyCollection<Expression>(list1);
MethodCallExpression right1 = Expression.Call(null, mi1, datarow1, constant1);
Expression left1 = Expression.Parameter(type, "Field1");
var expression1 = Expression.Assign(left1, right1);
MethodInfo mi2 = typeof(DataRowExtensions).GetMethod("Field", new Type[] { typeof(DataRow), typeof(int) });
mi2 = mi2.MakeGenericMethod(type);
List<Expression> list2 = new List<Expression>();
ParameterExpression datarow2 = Expression.Parameter(type, "datarow");
ConstantExpression constant2 = Expression.Constant(0, typeof(int));
list2.Add(datarow2);
list2.Add(constant2);
ReadOnlyCollection<Expression> collection2 = new ReadOnlyCollection<Expression>(list2);
MethodCallExpression right2 = Expression.Call(null, mi2, datarow2, constant2);
Expression left2 = Expression.Parameter(type, "Field2");
var expression2 = Expression.Assign(left2, right2);
List<Expression> bindings = new List<Expression>();
bindings.Add(expression1);
bindings.Add(expression2);
var newInit = Expression.New(typeof(object));
var init = Expression.NewArrayInit(type, bindings);
var dr = Expression.Parameter(type, "dr");
var linq = Expression.Lambda<Func<DataRow, DataRow>>(init, dr);

但是，它编译时有几个问题:

• expression1是(Field1 = datarow.Field(0))而不是Field1 = datarow.Field<int>(0)
• 表达2相同
• 抛出一个运行时异常:'System.Data.DataRow[]' cannot be used for return type 'System.Data.DataRow'在var linq = Expression.Lambda...
行

你能帮帮忙吗?

@George我认为我不需要类型字典，因为我有一组预定义的类型。