C# 动态编译LINQ查询以验证字典值

让我们假设我们需要查询一个实体列表，但我们不知道非常动态的条件，实体中有字典和简单字段，让这成为下一个实体地址（为了简单起见，我只留下了一个属性）

公共类地址
{
#地区公众成员
/// 
///额外的数据字段值
/// 
公共IDictionary DataFieldValues{get；set；}
公共字符串City{get；set；}
#端区
}

现在，如果我们在我得到实现时查询一个名为City的固定字段：

   private static Expression<Func<Address, bool>> BuildLambdaForAQueryItem(string caption, string value)
        {
            ParameterExpression param = Expression.Parameter(typeof(Address), caption);
            BinaryExpression body = Expression.Equal(Expression.PropertyOrField(param, caption),
                                                     Expression.Constant(value,
                                                                         typeof(Address).GetProperty(
                                                                             caption).PropertyType));
            return Expression.Lambda<Func<Address, bool>>(body, param);
        }

private static Expression我认为您希望对两个相关谓词表达式使用（短路和）来构造表达式树的主体

var body = Expression.AndAlso(keyExists, valueCorresponds);
return Expression.Lambda<Func<Address, bool>>(body, dataFields);

但在这种情况下，这是巨大的杀伤力；我的建议是使用我的第一个样品。
你说得对，谢谢。但是我仍然不明白为什么我以前的实现没有成功
private static Expression<Func<Address, bool>> BuildLambdaForAnExtraField(PostedQueryItem queryItem)
{
    ParameterExpression dataFields = Expression.Parameter(typeof(Address), "x");
    var dictionaryExpression = Expression.PropertyOrField(dataFields, "DataFieldValues");
    var keyExists = Expression.Call(dictionaryExpression, "ContainsKey", null, Expression.Constant(queryItem.Caption));

    Expression dictionaryAccessExpr = Expression.Property(dictionaryExpression, "Item",
                                                           Expression.Constant(queryItem.Caption));
    var valueCorresponds = Expression.Equal(dictionaryAccessExpr, Expression.Constant(queryItem.Value));

    return Expression.Lambda<Func<Address, bool>>(keyExists, dataFields).And(
      Expression.Lambda<Func<Address, bool>>(valueCorresponds, dataFields));
}

var body = Expression.AndAlso(keyExists, valueCorresponds);
return Expression.Lambda<Func<Address, bool>>(body, dataFields);

return Expression.Lambda<Func<Address, bool>>(keyExists, dataFields)
                 .And(Expression.Lambda<Func<Address, bool>>(valueCorresponds, dataFields))
                 .Expand();