如何通過LINQ中的字符串枚舉過濾C＃

Question

有沒有辦法如何使用字符串篩選數據與枚舉屬性？

這是我在服務層的功能，它需要2個參數用於尋呼功能，第三個參數用於按其狀態過濾項目。

我想這樣做projects.Where(x => x.Status == status)，但它會拋出錯誤，因爲我無法將枚舉與字符串進行比較。有沒有解決方法？

public async Task<ListResult<ProjectDTO>> GetListedProjects(int pageSize, int pageNumber, string status) 
{ 
    var projects = await unitOfWork.ProjectRepository.Get(); 
    //i cannot filter like this 
    projects.Where(x => x.Status == status); 
    var orderedProjects = projects.OrderBy(x => x.Name); 

    var projectList = orderedProjects.ToPagedList(pageNumber, pageSize); 

    var data = projectList.Select(x => ToDTO.ProjectBuild(x)).ToList(); 
    return new ListResult<ProjectDTO> { Data = data, TotalCount = projectList.TotalItemCount }; 
} 

這裏是我的項目模型：

public class Project : ManagementBaseClass 
{ 
    [Key] 
    public int Id { get; set; } 
    public Status Status { get; set; } 
    public Priority Priority { get; set; } 
    //etc just deleted more properties to make this cleaner 
} 

這是我的枚舉，我使用的項目分配狀態，任務等

public enum Status 
{ 
    New = 1, 
    Active = 2, 
    OnHold = 3, 
    Testing = 4, 
    Finished = 5, 
    Dropped = 6 
} 

Answer 1

可以分析字符串的枚舉相當於

很明顯，這段代碼是一個粗略的草稿，給你一個想法，並設置你在正確的軌道上，您必須對Parse執行空檢查以防止異常，或使用TryParse。

public async Task<ListResult<ProjectDTO>> GetListedProjects(int pageSize, int pageNumber, string status) 
{ 
    var projects = await unitOfWork.ProjectRepository.Get(); 
    //i cannot filter like this 
    projects.Where(x => x.Status == (Status)Enum.Parse(typeof(Status), status)); 
    var orderedProjects = projects.OrderBy(x => x.Name); 

    var projectList = orderedProjects.ToPagedList(pageNumber, pageSize); 

    var data = projectList.Select(x => ToDTO.ProjectBuild(x)).ToList(); 
    return new ListResult<ProjectDTO> { Data = data, TotalCount = projectList.TotalItemCount }; 
} 

Answer 2

你傳遞string這樣：

public async Task<ListResult<ProjectDTO>> GetListedProjects(int pageSize, int pageNumber, string status) 
{ 
    var projects = await unitOfWork.ProjectRepository.Get(); 
    //i cannot filter like this 
    projects.Where(x => x.Status == status); 
    var orderedProjects = projects.OrderBy(x => x.Name); 

    var projectList = orderedProjects.ToPagedList(pageNumber, pageSize); 

    var data = projectList.Select(x => ToDTO.ProjectBuild(x)).ToList(); 
    return new ListResult<ProjectDTO> { Data = data, TotalCount = projectList.TotalItemCount }; 
} 

當你要傳遞枚舉

public async Task<ListResult<ProjectDTO>> GetListedProjects(int pageSize, int pageNumber, Status status) 

你也可以傳遞字符串，並創建一個Status變量並使用一些switch語句，你可以將它設置爲正確的枚舉。一些答案顯示，我不喜歡將string轉換爲enum。在我看來，容易出錯的是，你最好試着或者A）將字符串解析爲Status或B）只傳入Status枚舉以避免任何衝突。

Answer 3

在您撥打projects.Where(x => x.Status == status);之前，您應該嘗試將該字符串值status解析到狀態枚舉中。

您可以使用Enum.Parse，如果解析失敗，則拋出異常，或者您可以使用Enum.TryParse，根據解析操作的成功/失敗返回bool。

Answer 4

可以解析字符串值：

private static TEnum? GetEnum<TEnum>(string value) where TEnum : struct 
{ 
    TEnum result; 

    return Enum.TryParse<TEnum>(value, out result) ? (TEnum?)result : null; 
} 

public async Task<ListResult<ProjectDTO>> GetListedProjects(int pageSize, int pageNumber, string status) 
{ 
    var projects = await unitOfWork.ProjectRepository.Get(); 
    //i cannot filter like this 
    projects.Where(x => x.Status == GetEnum<Status>(status)); 
    var orderedProjects = projects.OrderBy(x => x.Name); 

    var projectList = orderedProjects.ToPagedList(pageNumber, pageSize); 

    var data = projectList.Select(x => ToDTO.ProjectBuild(x)).ToList(); 
    return new ListResult<ProjectDTO> { Data = data, TotalCount = projectList.TotalItemCount }; 
}