主页 / coding / 问题 / 76920437
Accepted
Salomé
Asked: 2023-08-17 17:58:08 +0800 CST

如何将 select 语句详细信息提取到不同的方法中仍然保持急切加载？

  • 772

在实体框架中，我可以在将属性添加到 select 方法时显式加载属性，如下所示：

var workhours = dbContext.WorkHours
    .Select(w => new WorkHourLookupDto()
        {
            Id = w.Id,
            StartTime = w.StartTime,
            EndTime = w.EndTime,
            RecreationInMinutes = w.RecreationInMinutes,
            TotalWorkHoursInMinutes = w.TotalWorkHoursInMinutes,
            Customer = new CustomerMiniDto
            {
                Id = w.Customer.Id,
                Name = w.Customer.Name
            },
            Description = w.Description
        })
    .ToList();

var workhours2 = dbContext.WorkHours
    .Select(w => _factory.CreateLookUpDto(w))
    .ToList();

现在工作时间创建以下选择查询：

exec sp_executesql N'SELECT [w].[Id], [w].[StartTime], [w].[EndTime], [w].[RecreationInMinutes], [w].[CompanyId], [w].[Created], [w].[CreatedBy], [w].[CustomerId], [w].[Description], [w].[LastModified], [w].[LastModifiedBy], [w].[UserId], [t].[Id], [t].[Name]
FROM [WorkHours] AS [w]
INNER JOIN (
    SELECT [c].[Id], [c].[Name]
    FROM [Customers] AS [c]
    WHERE [c].[CompanyId] = @__ef_filter__CompanyId_2
) AS [t] ON [w].[CustomerId] = [t].[Id]
WHERE ([w].[CompanyId] = @__ef_filter__CompanyId_0) AND ([w].[UserId] = @__ef_filter__p_1)',N'@__ef_filter__CompanyId_2 nvarchar(4000),@__ef_filter__CompanyId_0 nvarchar(4000),@__ef_filter__p_1 uniqueidentifier',@__ef_filter__CompanyId_2=N'3AD04E77-9654-4BBB-A8E8-4DE1335A7516',@__ef_filter__CompanyId_0=N'3AD04E77-9654-4BBB-A8E8-4DE1335A7516',@__ef_filter__p_1='8220F8B8-720D-42E8-9357-2256470EA206'

workhours2 创建查询：

exec sp_executesql N'SELECT [w].[Id], [w].[CompanyId], [w].[Created], [w].[CreatedBy], [w].[CustomerId], [w].[Description], [w].[EndTime], [w].[LastModified], [w].[LastModifiedBy], [w].[RecreationInMinutes], [w].[StartTime], [w].[UserId]
FROM [WorkHours] AS [w]
WHERE ([w].[CompanyId] = @__ef_filter__CompanyId_0) AND ([w].[UserId] = @__ef_filter__p_1)',N'@__ef_filter__CompanyId_0 nvarchar(4000),@__ef_filter__p_1 uniqueidentifier',@__ef_filter__CompanyId_0=N'3AD04E77-9654-4BBB-A8E8-4DE1335A7516',@__ef_filter__p_1='8220F8B8-720D-42E8-9357-2256470EA206'

工厂是这样的：

public WorkHourLookupDto CreateLookUpDto(WorkHour workHour)
{
    return new()
    {
        Id = workHour.Id,
        StartTime = workHour.StartTime,
        EndTime = workHour.EndTime,
        RecreationInMinutes = workHour.RecreationInMinutes,
        TotalWorkHoursInMinutes = workHour.TotalWorkHoursInMinutes,
        Customer = _customerFactory.CreateMiniDto(workHour.Customer),
        Description = workHour.Description
    };
}

public CustomerMiniDto CreateMiniDto(Customer customer)
{
    if(customer != null)
        return new()
        {
            Id = customer.Id,
            Name = customer.Name
        };

    return new();
}

为什么将查询提取到不同的类（即方法）时会有所不同？

.net

1 个回答

  1. Best Answer

    您需要返回一个Expressionof 类型Func<WorkHour, WorkHourLookupDto>，即它接受 aWorkHour并返回 a WorkHourLookupDto。

    您不需要为此使用函数，您可以将其放入静态字段或属性中。

    private static Expression<Func<WorkHour, WorkHourLookupDto>> _createLookUpDto =
    workHour => new()
    {
        Id = workHour.Id,
        StartTime = workHour.StartTime,
        EndTime = workHour.EndTime,
        RecreationInMinutes = workHour.RecreationInMinutes,
        TotalWorkHoursInMinutes = workHour.TotalWorkHoursInMinutes,
        Customer = _customerFactory.CreateMiniDto(workHour.Customer),
        Description = workHour.Description
    };

private static Expression<Func<Customer, CustomerMiniDto>> _createMiniDto = 
    customer =>
    {
        if(customer != null)
            return new()
            {
                Id = customer.Id,
                Name = customer.Name
            };

        return new();
    }
}

    现在您只需直接传入表达式即可。

    var workhours2 = dbContext.WorkHours
    .Select(_createLookUpDto)
    .ToList();
    • 2

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