Question

抱歉我的英文。我在.NET 3.5中有LINQ to SQL查询，并希望在SearchDeviceExpression方法中重用DeviceExpression方法。像这样的东西

public static Expression<Func<DEVICE_TYPE, bool>> SearchDeviceExpression2(string s)
{
    return o => DEVICE_TYPE.DeviceExpression().Compile()(o) == s;
}

在运行时，我得到异常Method 'System.Object DynamicInvoke(System.Object[])' has no supported translation to SQL。所以没有该方法的翻译，但可能存在任何解决方法吗？

我的课。

[Table(Name = "DEVICE_TYPE_LOCAL")]
public class DEVICE_TYPE
{
    [Column]
    public string DEV_CODE
    {
        get;
        set;
    }
    [Column]
    public string DEVICE_NAME
    {
        get;
        set;
    }
    [Column]
    public string DEVICE_MARK
    {
        get;
        set;
    }

    public static Expression<Func<DEVICE_TYPE, string>> DeviceExpression()
    {
        return o => "(" + o.DEV_CODE + ") " + o.DEVICE_NAME + " " + o.DEVICE_MARK;
    }

    public static Expression<Func<DEVICE_TYPE, bool>> SearchDeviceExpression(string s)
    {
        return o => "(" + o.DEV_CODE + ") " + o.DEVICE_NAME + " " + o.DEVICE_MARK == s;
    }
}

Answer 1

您必须从表达式DeviceExpression返回创建一个新表达式，并返回一个返回字符串的表达式，然后您必须执行该表达式并将参数传递给它。像这样：

    public Expression<Func<string>> DeviceExpression()
    {
        return () => "(" + DEV_CODE + ") " + DEVICE_NAME + " " + DEVICE_MARK;
    }

    public Expression<Func<string,bool>> SearchDeviceExpression()
    {
        Expression<Func<string,string>> exp = (string s) => s;
        return Expression.Lambda<Func<string, bool>>(Expression.Equal(DeviceExpression().Body, exp.Body), exp.Parameters[0]);
    }

以下是如何执行它

    var t = new DEVICE_TYPE();
    t.DEV_CODE = "a";
    t.DEVICE_NAME = "b";
    t.DEVICE_MARK = "c";

    Console.Write(t.SearchDeviceExpression().Compile().Invoke("(a) b c"));

重用lambda表达式

1 个答案: