在每次创建产品时都将创建重复的数据类型 [英] Duplicate DataType is being created on every Product Creation

问题描述

我有一个产品模型，允许用户为他们的产品定义自己的自定义"字段.这可以通过3个表/模型来完成. Product模型，其中包含CustomProductProperty模型的IEnumerable枚举.每个CustomProductPropertyModel中的DataType是DataType模型的外键.此DataType模型是用户定义可用字段的地方.

I have a Product Model that allows users to define their own Custom fields for their Product. This is accomplished by have 3 tables/models. The Product model which contains an IEnumerable enumeration of CustomProductProperty models. in each CustomProductPropertyModel is a foreign key to a DataType model. This DataType model is where users define what fields are available.

我遇到的问题是，每当用户创建一个新产品时，就会创建一组新的DataType.如何处理数据，以使CustomProductProperty指向现有的DataType而不创建新的DataType?

The problem I am having is that everytime a user creates a new Product, a new set of DataType is created. How do I handle the data so that The CustomProductProperty points to an existing DataType and not creating a new one?

[Table("Product")]
public class Product
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ProductID { get; set; }
    public int ProductTypeID { get; set; }
    [Display(Name = "Product Name")]
    public string ProductName { get; set; }
    [ForeignKey("ProductTypeID")]
    [Display(Name = "Product Type")]
    public virtual ProductType ProductType { get; set; }
    public virtual ICollection<CustomProductProperty> CustomProperties { get; set; } 
}

[Table("CustomProductProperty")]
public class CustomProductProperty
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int CustomPropertyID { get; set; }

    public int CustomDataTypeID { get; set; }
    [ForeignKey("CustomDataTypeID")]
    public CustomDataType DataType { get; set; }

    public int ProductID { get; set; }
    [ForeignKey("ProductID")]
    public virtual Product Product { get; set; }

    public string PropertyValue { get; set; }
}

[Table("CustomDataType")]
public class CustomDataType
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int CustomTypeID { get; set; }
    public string PropertyName { get; set; }
    public CustomDataTypes DataType { get; set; }
    public int ModuleID { get; set; }
    [ForeignKey("ModuleID")]
    public Module Module { get; set; }
}

在创建表单中，我为DataType.CustomTypeID添加了@Html.HiddenFor()，并在调试时包含了它，但是当我添加到dbcontext中时，它会创建一个全新的DataType

In the creation form I included a @Html.HiddenFor() for DataType.CustomTypeID and when debugging, it is included but when I add to my dbcontext, it creates a brand new DataType

if (ModelState.IsValid)
    {
        db.Products.Add(productViewModel.Product);
        db.SaveChanges();
        return RedirectToAction("Index");
    }

用于创建产品的表单如下.

The form for creating a product is as follows.

<table class="basic_info_tbl">
    <tr>
        <th>@Html.LabelFor(model => model.Product.ProductName):</th>
        <td>@Html.TextBoxFor(model => model.Product.ProductName) </td>
        <th>@Html.LabelFor(model => model.Product.ProductType):</th>
        <td>@Html.DropDownListFor(model => model.Product.ProductTypeID, Model.ProductTypes)</td>
        @Html.EditorFor(model => model.Product.CustomProperties)
    </tr>
</table>

使用编辑器模板:

<tr>
        @Html.HiddenFor(model => model.DataType.CustomTypeID)
    <th>@Model.DataType.PropertyName</th>
    <td>@Html.TextBoxFor(model => model.PropertyValue)</td>
</tr>

推荐答案

来自Lerman&米勒的书 DbContext :

From Lerman & Miller's book DbContext:

添加图的根将导致 要在上下文中注册为新实体的图形.这种行为是一样的 如果您使用DbSet.Add或将实体的State属性更改为Added.一旦所有 实体由状态管理器跟踪，您可以然后围绕图表进行操作， 为每个实体指定正确的状态.

adding the root of a graph will cause every entity in the graph to be registered with the context as a new entity. This behavior is the same if you use DbSet.Add or change the State property for an entity to Added. Once all the entities are tracked by the state manager, you can then work your way around the graph, specifying the correct state for each entity.

(我的重点)

因此，在db.Products.Add(productViewModel.Product)之后，对象图中的CustomDataType对象也是Added.

So after db.Products.Add(productViewModel.Product) also the CustomDataType objects in the object graph are Added.

Add()之后，您应该遍历对象图

After the Add() you should loop through the object graph

foreach (var dt in productViewModel.Product.CustomProperties
                                   .Select(x => x.DataType).ToList())
{
    Entry(dt).State = EntityState.Unchanged;
}

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