根據另一個屬性c#運算式樹的值獲取引數

我有兩節課：

class JoinedMapVoucher
{
    public string Code1 { get; set; }
    public string Code2 { get; set; }
    public string Code3 { get; set; }
    public DL DL1 { get; set; }
    public DL DL2 { get; set; }
    public DL DL3 { get; set; }
    public DL DL4 { get; set; }
}
class DL
{
    public long DLTypeRef { get; set; }
}

在這里，我有一個字典，其中鍵是 DLTypeRef，值是不應為空的代碼，例如在此示例中，如果 DLTypeRef 為 5，則 Code1 屬性應具有值且不能為空。我想做的是從字典中動態獲取不應為空的代碼。然后我想從 JoinedMapVoucher 型別中獲取該代碼并檢查它是否為空。在下面的代碼中，我寫了我想從字典中獲取代碼的注釋，然后從 JoinedMapVoucher 引數中獲取該屬性，但它不起作用。

 var dic = new Dictionary<long, string>();
            dic.Add(5, "Code1");
            dic.Add(-1, "NullCode");
            var dicConst = Expression.Constant(dic);
    
            var list = Expression.Constant(new List<long> { 1, 2, 3, 4, 5 });
            var defaultDL = new DL { DLTypeRef = -1, Id = -1 };
            var foos = new List<JoinedMapVoucher> {new JoinedMapVoucher { DL2 = new DL { DLTypeRef = 5, Id = 55 } } }.AsQueryable();
            var containsMethod = typeof(List<long>).GetMethod(nameof(List<long>.Contains), new[] { typeof(long) });
    
            var parameter = Expression.Parameter(typeof(JoinedMapVoucher), "JoinedMapVoucher");
    
            for (var i = 1; i <= 4; i  )
            {
                
                var dl = Expression.PropertyOrField(parameter, "DL"   i.ToString());
                var actualDL = Expression.Coalesce(dl, Expression.Constant(defaultDL));
                var dlTypeRef = Expression.PropertyOrField(actualDL, "DLTypeRef");
                var or1 = Expression.Or(Expression.Equal(dlTypeRef, Expression.Constant((long)-1)), Expression.Not(Expression.Call(list, containsMethod, dlTypeRef)));
    
                
                var dicGetItemMethod = typeof(Dictionary<long, string>).GetMethod("get_Item", new[] { typeof(long) });
                var getCode = Expression.Constant(Expression.Call(dicConst, dicGetItemMethod, dlTypeRef)); **//here this call should return code from dictionary which it can be Code5 or NullCode**

               **var needCode=Expression.PropertyOrFeild(parameter,getCode) // then i want to get Code property from parameter dynamically**
                    
                
    
                var lambda = Expression.Lambda<Func<JoinedMapVoucher, bool>>(or1, new ParameterExpression[] { parameter });
                Console.WriteLine(lambda.Body);
                foos = foos.Where(lambda);
            }

如何在需要代碼變數中動態獲取屬性？

uj5u.com熱心網友回復：

您需要構建一個 switch 陳述句，該陳述句將打開getCode值并回傳相應的屬性。沿著這條線的東西：

var getCode = Expression.Call(dicConst, dicGetItemMethod, dlTypeRef);
SwitchExpression switchExpr =
    Expression.Switch(
        getCode,
        Expression.Constant("-1"), // default case when none is matched
        new SwitchCase[]
        {
            Expression.SwitchCase( // switch case for "Code1" returned from dict
                Expression.PropertyOrField(parameter, nameof(JoinedMapVoucher.Code1)),
                Expression.Constant( nameof(JoinedMapVoucher.Code1))
            ),
            Expression.SwitchCase( // switch case for "NullCode" returned from dict
                Expression.PropertyOrField(parameter, nameof(JoinedMapVoucher.Code2)),
                Expression.Constant("NullCode")
            ),
            
        }
    );

這應該代表在您的 lambda 中生成的內容：

var code = dictionary[dlTypeRef];
switch (code)
{
     case "Code1":
         return JoinedMapVoucher.Code1;
     case NullCode:
         return JoinedMapVoucher.Code2;
     default:
         return "-1";
}

標籤：C＃ 。网 林克 拉姆达 表达式树

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