BlazorWebAssembly GetFromJsonAsync未序列化子集合

Question

问题是，为什么当我用HttClient.GetFromJsonAsync从客户端调用api时，实体没有子集合？。我从浏览器调用api，JSON文本有集合，但在对象上没有。

这是我的实体代码：

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;
namespace excelnobleza.shared.Models.Tablas.Produccion
{
[Table("Lineas")]
public class Linea
{
public int Id { get; set; }
public string Nombre { get; set; }
public string Responsable { get; set; }
public string EmailResponsable { get; set; }
public virtual ICollection<Maquina> Maquinas { get; } = new HashSet<Maquina>();
public override string ToString() => this.Nombre;
}
public class Maquina
{
public int Id { get; set; }
[Required(ErrorMessage = "El nombre de la Maquina es requerido")]
public string NombreMaquina { get; set; }
[Required(ErrorMessage = "La Linea a la que pertenece la maquina es requerida")]
[ForeignKey("Linea")]
public int? Linea_Id { get; set; }

public virtual Linea Linea { get; set; }
}
}

我为API创建了一个控制器，返回all的代码是：

// GET: api/Lineas
[HttpGet]
public async Task<ActionResult<Linea[]>> GetLineas()
{
return await _context.Lineas.Include(o=> o.Maquinas).ToArrayAsync();
}

这会返回类似JSON的：

[
{
"Id":1,
"Nombre":"SCHIAVI",
"Responsable":"JOSUE TORRES",
"EmailResponsable":"jtorres",
"Maquinas":[
{
"Id":1,
"NombreMaquina":"SCHIAVI",
"ModeloMaquina":null,
"TipoMaquina_Id":1,
"TipoMaquina":null,
"Linea_Id":1
},
{
"Id":2,
"NombreMaquina":"Titan 1",
"ModeloMaquina":null,
"TipoMaquina_Id":3,
"TipoMaquina":null,
"Linea_Id":1
},
{
"Id":3,
"NombreMaquina":"Simplex",
"ModeloMaquina":null,
"TipoMaquina_Id":2,
"TipoMaquina":null,
"Linea_Id":1
},
{
"Id":4,
"NombreMaquina":"Brazileña",
"ModeloMaquina":null,
"TipoMaquina_Id":8,
"TipoMaquina":null,
"Linea_Id":1
}
]
},
{
"Id":2,
"Nombre":"WINDMOLLER",
"Responsable":"ERASMO CARRASCO",
"EmailResponsable":"ecarrasco",
"Maquinas":[
{
"Id":5,
"NombreMaquina":"WINDMOLLER",
"ModeloMaquina":null,
"TipoMaquina_Id":1,
"TipoMaquina":null,
"Linea_Id":2
},
{
"Id":6,
"NombreMaquina":"TITAN 2",
"ModeloMaquina":null,
"TipoMaquina_Id":3,
"TipoMaquina":null,
"Linea_Id":2
},
{
"Id":17,
"NombreMaquina":"Super Simplex",
"ModeloMaquina":null,
"TipoMaquina_Id":2,
"TipoMaquina":null,
"Linea_Id":2
}
]
}
]

RazorCode是：

@page "/lineas"
@inject HttpClient client
@inject IJSRuntime js
@using excelnobleza.shared.Models.Tablas.Produccion 
<h3>Lineas</h3>
<div class="form-group">
<a class="btn btn-success" href="lineas/create"><i class="oi oi-plus"></i> Crear</a>
</div>
@if (Lineas == null)
{
<h3>Loading...</h3>
}
else if (Lineas.Length == 0)
{
<h3>No se encontraron</h3>
}
else
{
<table class="table table-striped">
<thead>
<tr>
<th>Id</th>
<th>Nombre</th>
<th>Responsable</th>
<th>Email Responsable</th>
<th></th>
</tr>
</thead>
<tbody>
@foreach (Linea lin_ in Lineas)
{
<tr>
<td>@lin_.Id</td>
<td>@lin_.Nombre</td>
<td>@lin_.Responsable</td>
<td>    
@foreach (Maquina maq in lin_.Maquinas)
{
<h4>@maq.NombreMaquina - @maq.ModeloMaquina</h4>
}
</td>    
<td>
<a class="btn btn-success" href="lineas/edit/@lin_.Id">Edit</a>
</td>
</tr>
}
</tbody>
</table>
}
@code {
Linea[] Lineas;    
protected override async Task OnInitializedAsync()
{
Console.WriteLine("getting Lineas...");
Lineas = await client.GetFromJsonAsync<Linea[]>("api/lineas");
Console.WriteLine(System.Text.Json.JsonSerializer.Serialize(Lineas));// in this line i try to see the object string, but not have the collection
}
}

但是；lin_；对象未显示"的集合；Maquinas"(

已编辑-问题已解决实体将Icollection更改为List并设置为非只读属性

[Table("Lineas")]
public class Linea
{
public int Id { get; set; }
public string Nombre { get; set; }
public string Responsable { get; set; }
public string EmailResponsable { get; set; }
public virtual List<Maquina> Maquinas { get; set; } = new List<Maquina>();
public override string ToString() => this.Nombre;
}

Answer 1

问题由以下原因引起：

public virtual ICollection<Maquina> Maquinas { get; } = new HashSet<Maquina>();

没有setter，因此JSON反序列化程序无法设置该属性。Maquinas是JSON文档中的一个数组，因此最好的类型是List<Maquina>:

public List<Maquina> Maquinas { get;set; } 

如果需要延迟加载，则签名public virtual ICollection<Maquina> Maquinas仅由EF Core需要。在这种情况下，EF Core生成一个覆盖Maquinas的代理类，并仅在客户端代码尝试访问相关实体时才加载这些实体。当前代码通过急切地加载所有项目