c# - 无法在选择列表中保存多个选择 - asp.net core web 应用程序 razor 页面

Question

在这里，我可以在创建页面上绑定(bind)多选选择列表。

<select id="multiple" asp-for="SecurityLog.Officer" multiple="multiple" class="selectpicker form-control" asp-items="ViewBag.Officer">
</select>

public IActionResult OnGetAsync()
{                    
     ViewData["Officer"] = new SelectList(_context.Officer.Where(a => a.Active == "Y"), "ID", "FullName");

     return Page();
}

我遇到的最大问题是我正在尝试编辑/发布值，但我的模型中没有可以绑定(bind)的直接字段。

我在这里找到了一个很好的例子，但它只向您展示如何保存 1 个选择。 https://www.learnrazorpages.com/razor-pages/forms/select-lists

我的 SecurityLog 模型有这个

public virtual Officer Officer { get; set; }

我的军官模型有这个

namespace SecurityCore.Models
{
    public class Officer
    {
        [Required]
        public int ID { get; set; }

        [Required]
        [Display(Name = "Officer's First Name")]
        public string FirstName { get; set; }

        [Required]
        [Display(Name = "Officer's Last Name")]
        public string LastName { get; set; }

        [Display(Name = "Officer's Name")]
        public string FullName { get; set; }

        [Required]
        public string Active { get; set; }        
    }
}

我没有 SecurityLogOfficer 模型。我需要一个吗？

这是我的数据库架构和示例结果

如有任何帮助，我们将不胜感激!

* 更新 *

感谢您建议绑定(bind)到列表并将 asp-for 更改为该列表。这是我更新的代码。 SelectedOfficerIds 确实存储所选的 ID。

<select id="multiple" asp-for="SelectedOfficerIds" multiple="multiple" class="selectpicker form-control" asp-items="ViewBag.Officer">    
</select>

我正在发布到两个不同的数据库(1 条记录应发送到 SecurityLog，多条记录应发送到 SecurityLogOfficer)，但由于我调用 savechanes() 两次，它实际上将多条记录发送到 SecurityLog 数据库，并在第二次 for 循环保存我收到错误

Cannot insert explicit value for identity column in table 'SecurityLogOfficer' when IDENTITY_INSERT is set to OFF

_context.SecurityLog.Add(SecurityLog);
//We need to ensure we have the ID of the newly posted event
_context.SaveChanges();

int tempSecurityLogID = SecurityLog.ID;

for (int i = 0; i < SelectedOfficerIds.Length; i++)
{                
     SecurityLogOfficer.SecurityLogID = tempSecurityLogID;
     SecurityLog = null;

     SecurityLogOfficer.OfficerID = SelectedOfficerIds[i];
     _context.SecurityLogOfficer.Add(SecurityLogOfficer);                
     await _context.SaveChangesAsync();
}            

Message = "Entry added successfully!";

有没有办法清除SecurityLog的_context，这样我只发布一次，如何解决identity_insert问题？数据库 SecurityLogOfficer 已插入身份。

更新 2020 年 1 月 9 日

@XingZou - 感谢您的快速回复。我尝试执行您的步骤，一切都很顺利!!!

如果您不介意的话，我还有一个问题？我试图获取编辑页面上所选值的列表，但无法设置这些值。这是我到目前为止所尝试的...

这是我的编辑页面模型...

[BindProperty] 
public MultiSelectList GetExistingSelectedOfficerIds { get; set; }

public async Task<IActionResult> OnGetAsync(int? id)
{
    var i = _context.SecurityLogOfficer.Where(a => a.SecurityLogID == SecurityLog.ID);

        SecurityLogOfficers.AddRange(i);

        int[] GetExistingSelectedOfficerIds = new int[SecurityLogOfficers.Count];

        int itemCount = 0;
        foreach (var item in SecurityLogOfficers)
        {                
            GetExistingSelectedOfficerIds[itemCount] = item.OfficerID;
            itemCount++;
        }

        return Page();
}

这是我的编辑 Razor 页面...

<select id="multiple" asp-for= "GetExistingSelectedOfficerIds" multiple="multiple" class="selectpicker form-control" asp-items="ViewBag.Officer">
</select>
<span asp-validation-for="GetExistingSelectedOfficerIds" class="text-danger"></span>

Answer 1

您需要将下拉列表绑定(bind)到 int 列表而不是 object。

在 PageModel 中，添加一个新属性来存储所有选定的 Id:

[BindProperty]
public int[] SelectedOfficerIds { get; set; }

在 Razor Pages 上，将多选绑定(bind)到 SelectedOfficerIds

<form method="post">
    <div asp-validation-summary="ModelOnly" class="text-danger"></div>
    <div class="form-group">
        <label asp-for="SecurityLog.EventDate" class="control-label"></label>
        <input asp-for="SecurityLog.EventDate" class="form-control" />
        <span asp-validation-for="SecurityLog.EventDate" class="text-danger"></span>
    </div>
    <div class="form-group">
        <label class="control-label">Officers</label>
        <select id="multiple" asp-for="SelectedOfficerIds" multiple="multiple" class="selectpicker form-control" asp-items="ViewBag.Officer">
        </select>
    </div>

    <div class="form-group">
        <input type="submit" value="Create" class="btn btn-primary" />
    </div>
</form>

当您提交表单时，您将在帖子处理程序中获得安全日志的新官员 ID 列表。

更新 2020 年 1 月 9 日

There is no direct relationship between SecurityLog and Officer. There is a one-to-many relationship between SecurityLog and SecurityLogOfficer and a many-to-one relationship between SecurityLogOfficer and Officer.

根据你的描述，它是many-to-many relationships在SecurityLog 和Officer 之间。 1.删​​除SecurityLogOfficer的ID，现在使用复合 key

public class SecurityLogOfficer
{
    public int SecurityLogID { get; set; }
    public SecurityLog SecurityLog { get; set; }

    public int OfficerID { get; set; }
    public Officer Officer { get; set; }
}
public class Officer
{
    public int ID { get; set; }

    //other properties

    public List<SecurityLogOfficer> SecurityLogOfficers { get; set; }
}

public class SecurityLog
{
    public int ID { get; set; }

    //other properties

    public virtual List<SecurityLogOfficer> SecurityLogOfficers { get; set; }
}

2.配置多对多关系，如下所示。

public class RazorpagesCoreContext : DbContext
{
    public RazorpagesCoreContext (DbContextOptions<RazorpagesCoreContext> options)
        : base(options)
    {
    }


    public DbSet<Officer> Officer { get; set; }
    public DbSet<SecurityLog> SecurityLog { get; set; }
    public DbSet<SecurityLogOfficer> SecurityLogOfficer { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<SecurityLogOfficer>()
            .HasKey(t => new { t.SecurityLogID, t.OfficerID });

        modelBuilder.Entity<SecurityLogOfficer>()
            .HasOne(pt => pt.SecurityLog)
            .WithMany(p => p.SecurityLogOfficers)
            .HasForeignKey(pt => pt.SecurityLogID);

        modelBuilder.Entity<SecurityLogOfficer>()
            .HasOne(pt => pt.Officer)
            .WithMany(t => t.SecurityLogOfficers)
            .HasForeignKey(pt => pt.OfficerID);
    }
}

3.添加迁移并更新数据库。

Is there a way to clear out _context for SecurityLog so I only post once

4.在您的PageModel中，保存如下数据

[BindProperty]
public SecurityLog SecurityLog { get; set; }

public List<SecurityLogOfficer> SecurityLogOfficers { get; set; } = new List<SecurityLogOfficer>();

[BindProperty]
public int[] SelectedOfficerIds { get; set; }

public async Task<IActionResult> OnPostAsync()
    {
        _context.SecurityLog.Add(SecurityLog);
        foreach (var id in SelectedOfficerIds)
        {
            var item = new SecurityLogOfficer()
            {
                SecurityLog = SecurityLog,
                Officer = await _context.Officer.FirstOrDefaultAsync(s => s.ID == id),
            };
            SecurityLogOfficers.Add(item);
        }
        _context.SecurityLogOfficer.AddRange(SecurityLogOfficers);
        await _context.SaveChangesAsync();

        return RedirectToPage("./Index");
    }

更新 2020 年 1 月 10 日

要在编辑页面中获取多个选定值，请在获取处理程序中的 return Page() 之前使用以下代码

ViewData["Officer"] = new MultiSelectList(_context.Officers.Where(a => a.Active == "Y"), "ID", "FullName", GetExistingSelectedOfficerIds);