c# - 如何合并不同 switch case 下的方法调用，使代码通用或优化？

Question

我有一个从数据库中获取员工信息的方法。方法如下，带一个switch case

public void RetrieveEmployeeInfo(EmployeeInfoRequest request)
{
    EmployeeStandardInfoResponse response;
    int employeeId;
    switch (request.Type.ToLowerInvariant())
    {
        case "employeeid":
            //Some Logic
            response = GetEmployeeInfoFromDatabase(EmployeeSearchType.ByEmployeeID, employeeId);
            break;
        case "emailaddress":
            //Some Logic
            response = GetEmployeeInfoFromDatabase(EmployeeSearchType.ByEmailAddress, emailAddress:request.Id);
            break;
        default:
            return null;
    }
    return response;
}

“GetEmployeeInfoFromDatabase”的签名是

public EmployeeStandardInfoResponse GetEmployeeInfoFromDatabase(EmployeeSearchType employeeSearchType, dynamic value)
{
    //For simplicity I am returning employee info here
    return new EmployeeStandardInfoResponse();
}

下面是支持类和Enum

public enum EmployeeSearchType
{
    ByEmployeeID = 1,
    ByEmailAddress = 2
}

public class EmployeeInfoRequest
{
    public int Id;
    public string Type;
}

public class EmployeeStandardInfoResponse
{
    public int employeeReferenceId;
    public string employeeDepartment;
    public string employeePfDetails;
    public string employeeName;
    public string employeeEmailAddress;
    public string employeeAddress;
}

如何使 switch case 通用，这样我就不必在每种情况下都调用方法“GetEmployeeInfoFromDatabase”？

Answer 1

以下不是完整的解决方案；但足以帮助您实现目标。想法是:根据用户搜索条件，使用 lambda 表达式语法创建表达式树。在存储库中的 final方法中，您可以传递该表达式并解析它(比如获取数据库 sql 查询)以从数据库中获取信息。

public class Program
    {
        static void Main()
        {
            GetEmployeeInfoFromDatabase((e) => e.EmployeeEmail == "UserProvidedEmailAdderessGoesHere");
        }

        public EmployeeStandardInfoResponse static GetEmployeeInfoFromDatabase(Expression<Func<Employee,bool>> exprssion)
        {
           /* parse this exression to build query*/
           /* use as it is if using entity framework*/
        }
    }

    class Employee
    {
        public int EmployeeId { get; set; }
        public string EmployeeEmail { get; set; }
    }
}

对 this 的第二个/第三个答案stack over flow 帖子精美地描述了查询翻译逻辑的表达式。

您可以继续并进一步使其更具可重用性和通用性(不仅限于 Employee 实体)

public EmployeeStandardInfoResponse static GetEmployeeInfoFromDatabase<T>(Expression<Func<T,bool>> exprssion)
            {
               /* parse this expression to build query*/
               /* use as it is if using entity framework*/
            }