Entity Framework 用于计算的 Where 子句属性

Question

我有以下型号：

public class Account
{
    public Guid Id{ get; set; }

    [Filterable]
    public string Code{ get; set; }

    [Filterable]
    public string AccountStatus { get; set; }
}

属性 AccountStatus 的值是根据 StartDate 和 EndDate 的值计算的，所以在我的存储库中的 Linq 查询中，我有以下内容:

public IEnumerable<Account> Get(QueryClause<Account> queryClause, out ForGetCollectionOptions forGetCollectionOptions)
{
        using (_dbContext)
        {
            var result = (
              from account in _dbContext.Accounts
              select new Account
              {
               Id = account.ID,
               Code = account.Code.Trim(),
               AccountStatus = StatusCalculator.GetStatus(account.StartDate, account.EndDate)
               }
           ApplyFilterClause(ref result, queryClause.FilterClause);
        }
}

为了计算帐户状态，我们有以下内容： public 枚举状态 { 无效, 积极的，未来 }

public static class StatusCalculator
{
    public static string GetStatus(DateTime? startDate, DateTime? endDate)
    {
        var now = DateTime.Now;

        if (startDate != null && startDate > now)
        {
            return Status.Future.ToString().ToLower();
        }

        if (startDate != null && endDate == null)
        {
            return Status.Active.ToString().ToLower();
        }

        return Status.Inactive.ToString().ToLower();
    }
}

问题是，当我尝试过滤例如 'inactive' 的帐户状态时，我收到以下运行时间警告：

warn: Microsoft.EntityFrameworkCore.Query[20500]
  The LINQ expression 'where (GetStatus([account].StartDate, [account].EndDate) == "inactive")' could not be translated and will be evaluated locally.
 warn: Microsoft.EntityFrameworkCore.Query[20500]
  The LINQ expression 'Count()' could not be translated and will be evaluated locally.

因为计算的属性无法翻译，查询将在没有该条件的情况下发送并检索所有数据，然后在本地应用该过滤器，这会损害性能。

如何为 where 子句添加此属性的自定义翻译并排序和计数？

Answer 1

你计算属性的业务逻辑目前很简单，所以可以内联：

public IEnumerable<Account> Get(QueryClause<Account> queryClause, out ForGetCollectionOptions forGetCollectionOptions)
{
        using (_dbContext)
        {
            var result = (
              from account in _dbContext.Accounts
              select new Account
              {
               Id = account.ID,
               Code = account.Code.Trim(),
               AccountStatus = (account.StartDate != null && account.EndDate == null)
                                  ? "Active"
                                  : (account.StartDate != null && account.StartDate > DateTime.Now) 
                                     ? "Future"
                                     : "Inactive"
               }
           ApplyFilterClause(ref result, queryClause.FilterClause);
        }
}

这应该使 EF 能够将其转换为 CASE 语句，例如：

SELECT  foo
       ,(CASE 
          WHEN t.StartDate IS NOT NULL...
          WHEN t.StartDate IS NOT NULL AND t.StartDate > GetDate()
          ELSE ...
        )
FROM bar

Entity Framework 用于计算的 Where 子句属性

Entity Framework Where Clause for Calculated property

linq

expression

entity-framework

calculated-field

Entity Framework 用于计算的 Where 子句 属性

Entity Framework Where Clause for Calculated property

linq

expression

entity-framework

calculated-field

Entity Framework 用于计算的 Where 子句属性