使用EF6处理包含连接表的插入 [英] Handling inserts that include a junction table using EF6

问题描述

我正在设计一个表单，允许用户将基于结构的设计记录添加到数据库中。作为规范的一部分，用户希望能够从下拉列表中选择多个选项。在数据库中，我创建了设计表和一个查找表来存储选项。由于这是一对多的关系，因此我创建了一个联结表。

I'm designing a form that allows the user to add a design record based on a structure to a database. As part of the spec the users want to be able to choose multiple options from a dropdown. In my database I've created the design table and a lookup table to store the options. As this is a 1 to many to 1 relationship I've created a junction table.

Design table
-------------
designid,
option

Option table
------------
optionid,
optionname

DesignDesignOption table
------------------------
designid,
optionid

使用EF db first选项，我有2个模型称为design和option。 EF省略了联结表。

Using the EF db first option I have 2 models called design and option. EF has omitted the junction table.

从下拉列表中，我得到了一个ID后面的字符串数组，但该数组已被选择，但我不确定如何添加联接表的条目。是否需要查询数据库，根据ID从数据库中选择选项？我真的不知道该怎么做。

From the dropdown I'm getting a string array of id's back that have been chosen but I'm not sure how to go about adding the entry to the junction table. Do I have to query the db, select the options chosen from the database based on the id's? I really have no clue how to do this.

到目前为止，我的代码如下。到目前为止，我还没有添加处理联结表的代码：

My code so far is below. As yet I haven't added the code to handle the junction table:

public bool InsertDesign(Design design){
            if (!Validate(design)) {
                return false;
            }

            design.ModifiedDate = DateTime.Now;
            design.ModifiedByFullName = base.GetUsersFullName();
            design.ModifiedBy = base.GetUserLogin();

            _context.Designs.Add(design);
            _context.SaveChanges();

            return true;
        } 

推荐答案

我想，你有选项ID列表，并且在 Design 模型中应该有 Options 导航属性。然后，您有两个选择：

I suppose that, you have list of OptionIds and there should be Options navigation property at Design model. Then you have two options:

如您所述，根据ID列表选择选项：

As you stated, select options according to list of Ids:

var optionIds = ...;
// Get options from database
List<Option> options = _context
    .Options
    .Where(m => optionIds.Contains(m.OptionId))
    .ToList();
design.Options = options;

_context.Designs.Add(design);
_context.SaveChanges();

第二种选择：

如果不想从数据库中选择数据，则可以将添加选项的状态设置为不变；

Second option:

If you do not want to select data from database, then you can set state of added option to Unchanged;

using System.Data.Entity;

var optionIds = ...;

// Initialize options according to Ids
List<Option> optionList = new List<Option>();
optionIds.ForEach(m => optionList.Add(new Option { OptionId = m})));

// Set options of desing and add it to context
design.Options = optionList;
_context.Designs.Add(design);

// Set state of options to unchanged to not affect their data and save changes
optionList.ForEach(m => _context.Entry(m).State = EntityState.Unchanged);
_context.SaveChanges();

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