Blu*_*kes 4 c# odata entity-framework-core asp.net-core
开发环境
楷模
public class Computer
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Disk> Disks { get; set; }
}
public class Disk
{
public int Id { get; set; }
public string Letter { get; set; }
public float Capacity { get; set; }
public int? ComputerId { get; set; }
public virtual Computer Computer { get; set; }
}
托斯
public class ComputerDto
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<DiskDto> Disks { get; set; }
}
public class DiskDto
{
public string Letter { get; set; }
public float Capacity { get; set; }
}
EF 核心上下文
public class ComputerContext : DbContext
{
public DbSet<Computer> Computers { get; set; }
public DbSet<Disk> Disks { get; set;}
public ComputerContext(DbContextOptions<ComputerContext> options)
: base(options)
{
}
}
OData EDM 模型
private static IEdmModel GetEdmModel()
{
var builder = new ODataConventionModelBuilder();
builder.EntitySet<Computer>("Computers");
builder.EntitySet<Disk>("Disks");
builder.ComplexType<ComputerDto>();
builder.ComplexType<DiskDto>();
return builder.GetEdmModel();
}
ASP.NET 核心控制器
[Route("api/[controller]")]
[ApiController]
public class ComputersController : ControllerBase
{
private readonly ComputerContext context;
public ComputersController(ComputerContext context)
{
this.context = context;
}
[HttpGet]
[EnableQuery]
public IQueryable<ComputerDto> GetComputers()
{
return this.context.Computers.Select(c => new ComputerDto
{
Id = c.Id,
Name = c.Name,
Disks = c.Disks.Select(d => new DiskDto
{
Letter = d.Letter,
Capacity = d.Capacity
}).ToList()
});
}
}
此查询有效，但磁盘已扩展，因为我正在手动创建列表。
https://localhost:46324/api/computers?$filter=startswith(name,'t')
和输出
{
"@odata.context": "https://localhost:46324/api/$metadata#Collection(ODataPlayground.Dtos.ComputerDto)",
"value": [
{
"Id": 14,
"Name": "TestComputer1",
"Disks": [
{
"Letter": "C",
"Capacity": 234.40
},
{
"Letter": "D",
"Capacity": 1845.30
}
]
},
{
"Id": 15,
"Name": "TestComputer2",
"Disks": [
{
"Letter": "C",
"Capacity": 75.50
},
{
"Letter": "D",
"Capacity": 499.87
}
]
}
]
}
如果我然后尝试使用以下查询扩展“磁盘”，则会收到错误消息：
https://localhost:46324/api/computers?$filter=startswith(name,'t')&$expand=disks
错误
{
"error": {
"code": "",
"message": "The query specified in the URI is not valid. Property 'disks' on type 'ODataPlayground.Dtos.ComputerDto' is not a navigation property or complex property. Only navigation properties can be expanded.",
"details": [],
"innererror": {
"message": "Property 'disks' on type 'ODataPlayground.Dtos.ComputerDto' is not a navigation property or complex property. Only navigation properties can be expanded.",
"type": "Microsoft.OData.ODataException",
"stacktrace": "...really long stack trace removed for compactness..."
}
}
}
题
非dto输出
{
"@odata.context": "https://localhost:46324/api/$metadata#Collection(ODataPlayground.Dtos.ComputerDto)",
"value": [
{
"Id": 14,
"Name": "TestComputer1",
"Disks": [
{
"Id": 16,
"ComputerId": 14,
"Letter": "C",
"Capacity": 234.40
},
{
"Id": 17,
"ComputerId": 14,
"Letter": "D",
"Capacity": 1845.30
}
]
}
]
}
所需的输出（使用上面的 $filter 和 $expand 查询）
{
"@odata.context": "https://localhost:46324/api/$metadata#Collection(ODataPlayground.Dtos.ComputerDto)",
"value": [
{
"Id": 14,
"Name": "TestComputer1",
"Disks": [
{
"Letter": "C",
"Capacity": 234.40
},
{
"Letter": "D",
"Capacity": 1845.30
}
]
}
]
}
更新 #1
如果我将 Automapper 添加到组合中并尝试使用ProjectTo以下代码的方法：
//// Inject context and mapper
public ComputersController(ComputerContext context, IMapper mapper)
{
this.context = context;
this.mapper = mapper;
}
[HttpGet]
[EnableQuery]
public IQueryable<ComputerDto> GetComputers()
{
return this.context.Computers.ProjectTo<ComputerDto>(mapper.ConfigurationProvider);
}
我得到一个不同的错误：
InvalidOperationException: When called from 'VisitLambda', rewriting a node of type
'System.Linq.Expressions.ParameterExpression' must return a non - null value of the same type.
Alternatively, override 'VisitLambda' and change it to not visit children of this type.
我似乎能够将顶级类作为 dto 返回，只公开客户端可能需要的属性，但是否也可以公开并返回 dto 作为导航属性？
这是可能的，但您需要解决一些特定于建模和实现的问题。
第一，建模。OData 仅支持实体类型的集合导航属性。因此，为了将ComputerDto.Disks属性映射为导航属性，您需要创建DiskDto实体类型。这反过来又要求它有一把钥匙。因此，要么Id为其添加属性，要么将其他一些属性（例如，Letter）与其关联：
//builder.ComplexType<DiskDto>();
builder.EntityType<DiskDto>().HasKey(e => e.Letter);
现在该Disks属性将不包含在没有$expand选项的情况下，并且还将消除原始 OData 异常。
这是所有关于OData的EDM模型，并实现$expand了选项Disks。
下一个要解决的问题与 OData 和 EF Core 查询实现细节有关。运行过滤查询 (w/o $expand) 会产生所需的 JSON 输出（不Disks包括在内），但生成的 EF Core SQL 查询是
SELECT [c].[Id], [c].[Name], [d].[Letter], [d].[Capacity], [d].[Id]
FROM [Computers] AS [c]
LEFT JOIN [Disks] AS [d] ON [c].[Id] = [d].[ComputerId]
WHERE (@__TypedProperty_0 = N'') OR ([c].[Name] IS NOT NULL AND (LEFT([c].[Name], LEN(@__TypedProperty_0)) = @__TypedProperty_0))
ORDER BY [c].[Id], [d].[Id]
如您所见，它包括不必要的连接和列，这是低效的。
使用$expand选项，您会得到VisitLambda异常，该异常来自 EF Core 3.1 查询转换管道，由成员投影中的ToList()调用引起Disks，而这又是必需的，因为目标属性类型是ICollection<DiskDto>并且没有它，您会得到编译时错误。可以通过创建属性类型IEnumerable<DiskDto>并删除ToList()from 投影来解决，这将消除异常，但再次会产生更低效的 SQL 查询
SELECT [c].[Id], [c].[Name], [d].[Letter], [d].[Capacity], [d].[Id], @__TypedProperty_2, [d0].[Letter], [d0].[Capacity], CAST(1 AS bit), [d0].[Id]
FROM [Computers] AS [c]
LEFT JOIN [Disks] AS [d] ON [c].[Id] = [d].[ComputerId]
LEFT JOIN [Disks] AS [d0] ON [c].[Id] = [d0].[ComputerId]
WHERE (@__TypedProperty_0 = N'') OR ([c].[Name] IS NOT NULL AND (LEFT([c].[Name], LEN(@__TypedProperty_0)) = @__TypedProperty_0))
ORDER BY [c].[Id], [d].[Id], [d0].[Id]
所有这一切都意味着尝试直接通过 EF Core 投影查询使用 OData 查询是有问题的。
因此，作为实现问题的解决方案，我建议AutoMapper.Extensions.OData扩展：
ODataQueryOptions根据查询创建 LINQ 表达式并执行查询。
您需要的是安装包AutoMapper.AspNetCore.OData.EFCore，使用类似于此的 AutoMapper 配置（关键是启用空集合和显式扩展）
cfg.AllowNullCollections = true;
cfg.CreateMap<Computer, ComputerDto>()
.ForAllMembers(opt => opt.ExplicitExpansion());
cfg.CreateMap<Disk, DiskDto>()
.ForAllMembers(opt => opt.ExplicitExpansion());
（注意：使用这种方法，属性类型可以保留ICollection<DiskDto>）
并更改类似于此的控制器方法（关键是不要使用EnableQuery，添加选项参数并返回IEnumerable/ICollection而不是IQueryable）
using AutoMapper.AspNet.OData;
[HttpGet]
public async Task<IEnumerable<ComputerDto>> GetComputers(
ODataQueryOptions<ComputerDto> options) =>
await context.Computers.GetAsync(mapper, options, HandleNullPropagationOption.False);
现在两个输出都将如预期的那样，以及生成的 SQL 查询：
输出：
{
"@odata.context": "https://localhost:5001/api/$metadata#Collection(ODataTest.Dtos.ComputerDto)",
"value": [
{
"Id": 1,
"Name": "TestComputer1"
},
{
"Id": 2,
"Name": "TestComputer2"
}
]
}
SQL查询：
SELECT [c].[Id], [c].[Name]
FROM [Computers] AS [c]
WHERE [c].[Name] IS NOT NULL AND ([c].[Name] LIKE N't%')
$expand=disks输出：
{
"@odata.context": "https://localhost:5001/api/$metadata#Collection(ODataTest.Dtos.ComputerDto)",
"value": [
{
"Id": 1,
"Name": "TestComputer1",
"Disks": [
{
"Letter": "C",
"Capacity": 234.4
},
{
"Letter": "D",
"Capacity": 1845.3
}
]
},
{
"Id": 2,
"Name": "TestComputer2",
"Disks": [
{
"Letter": "C",
"Capacity": 75.5
},
{
"Letter": "D",
"Capacity": 499.87
}
]
}
]
}
SQL查询：
SELECT [c].[Id], [c].[Name], [d].[Id], [d].[Capacity], [d].[ComputerId], [d].[Letter]
FROM [Computers] AS [c]
LEFT JOIN [Disks] AS [d] ON [c].[Id] = [d].[ComputerId]
WHERE [c].[Name] IS NOT NULL AND ([c].[Name] LIKE N't%')
ORDER BY [c].[Id], [d].[Id]
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