我正在使用EF 4.1 Code First,我无法按照我认为应该能够的方式初始化数据。在下面的代码中,您将看到我有一个以Client开头的模型,它包含一系列相关对象。我加载每个对象类型并将其设置为其父对象。将数据加载到我的对象后,我尝试将顶级对象Client保存到数据库中。当我这样做时,我得到一个System.NullReferenceException。
EF不会深度加载吗?
我是否需要将每个对象集保存到数据库中,首先将它们相互关联,然后将它们重新保存到数据库中?如果我必须这样做,那么当它应该能够在一个查询中执行时,加载我的数据似乎会有很多连接。
任何建议或回答都将不胜感激。
下面是我的代码,下面是我的例外:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Entity;
namespace MyNameSpace
{
class Program
{
static void Main(string[] args)
{
Database.SetInitializer(new TimeServiceContextInitializer());
TimeServiceContext db = new TimeServiceContext();
var clients = db.Clients.ToList();
foreach (var client in clients)
{
Console.WriteLine("Client: {0}\r\nNumber of Sites: {1}\r\n", client.Name, client.Sites.Count);
}
}
}
// Initialize Database
public class TimeServiceContextInitializer : DropCreateDatabaseIfModelChanges<TimeServiceContext>
{
protected override void Seed(TimeServiceContext db)
{
List<Client> clients = new List<Client>();
Client client = new Client();
client.Name = "Achme Big Company";
Site site = new Site();
site.Name = "www.SampleSite.com";
Project project = new Project();
project.Name = "Schololarship Application Phase 1";
project.Description = "Create an application that allows student to apply for scholarship in the www.SampleSite.com web site.";
project.DateCreated = DateTime.Now.AddDays(-15);
project.StartDate = DateTime.Now.AddDays(-5);
project.DeadlineDate = DateTime.Now.AddDays(45);
project.Status = Status.In_Progress;
project.FixedFee = 40500.00m;
project.SpecialNotes = "This project has a firm deadline due to the fact that marketing information is already set to go out to advertize applying for scholarships online through the web site";
TimeEntry timeEntry = new TimeEntry();
timeEntry.EmployeeName = "Brian Johns";
timeEntry.TasksPerformed = "Started working on sceen mockups for the first page of the scholoarship application";
timeEntry.TimeRecorded = DateTime.Now.AddDays(-4).AddHours(10);
project.TimeEntries.Add(timeEntry); /// <---- --------------------------- GET System.NullReferenceException Exception Here -----------
timeEntry = new TimeEntry();
timeEntry.EmployeeName = "Brian Johns";
timeEntry.TasksPerformed = "Completed first section of form fields and started on the second section for the first page of the scholoarship application";
timeEntry.TimeRecorded = DateTime.Now.AddDays(-4).AddHours(11.5);
project.TimeEntries.Add(timeEntry);
timeEntry = new TimeEntry();
timeEntry.EmployeeName = "Brian Johns";
timeEntry.TasksPerformed = "Decided we needed to regroup fields so started modifying form layout to work better on the first page of the scholoarship application";
timeEntry.TimeRecorded = DateTime.Now.AddDays(-4).AddHours(13.25);
project.TimeEntries.Add(timeEntry);
timeEntry = new TimeEntry();
timeEntry.EmployeeName = "Brian Johns";
timeEntry.TasksPerformed = "Completed first form of the scholarship application. Started discussing the next form for step 2 of the scholarship application process";
timeEntry.TimeRecorded = DateTime.Now.AddDays(-4).AddHours(14);
project.TimeEntries.Add(timeEntry);
site.Projects.Add(project);
client.Sites.Add(site);
db.Clients.Add(client);
db.SaveChanges();
base.Seed(db);
}
}
// Context
public class TimeServiceContext : DbContext
{
public DbSet<Client> Clients { get; set; }
public DbSet<Site> Sites { get; set; }
public DbSet<Project> Projects { get; set; }
public DbSet<TimeEntry> TimeEntries { get; set; }
}
// Model Starts Here
public class Client
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Site> Sites { get; set; }
public DateTime DateCreated { get; set; }
}
public class Site
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Project> Projects { get; set; }
public int ClientId { get; set; }
public DateTime DateCreated { get; set; }
}
public enum Status { Not_Started, In_Progress, Completed };
public class Project
{
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public DateTime StartDate { get; set; }
public DateTime DeadlineDate { get; set; }
public DateTime CompletionDate { get; set; }
public decimal FixedFee { get; set; }
public decimal HourlyRate { get; set; }
public Status Status { get; set; }
public string SpecialNotes { get; set; }
public ICollection<TimeEntry> TimeEntries { get; set; }
public int SiteId { get; set; }
public DateTime DateCreated { get; set; }
}
public class TimeEntry
{
public int id { get; set; }
public string EmployeeName { get; set; }
public string TasksPerformed { get; set; }
public DateTime TimeRecorded { get; set; }
public int InvoiceNumber { get; set; }
public int ProjectId { get; set; }
}
}
Esception详情:
System.NullReferenceException未被用户代码处理
Message =对象引用未设置为对象的实例。
来源=控制台
堆栈跟踪:
at MyNameSpace.TimeServiceContextInitializer.Seed(TimeServiceContext db)in C:\ Users \ Justin \ Source Control \ CoutoTimeService \ Console \ Program.cs:第51行
在System.Data.Entity.DropCreateDatabaseIfModelChanges 1.InitializeDatabase(TContext context)
at System.Data.Entity.Database.<>c__DisplayClass2
1.b_ 0(DbContext c)
在System.Data.Entity.Internal.InternalContext。&lt;&gt; c _DisplayClass5.b_ 3()
在System.Data.Entity.Internal.InternalContext.PerformInitializationAction(Action action)
在System.Data.Entity.Internal.InternalContext.PerformDatabaseInitialization()
在System.Data.Entity.Internal.LazyInternalContext.b _4(InternalContext c)
在System.Data.Entity.Internal.RetryAction`1.PerformAction(TInput输入)
InnerException:
答案 0 :(得分:1)
将一个构造函数添加到项目类
Project(){
TimeEntries = new HashSet<TimeEntry>();
}
你也可以使用像这样的对象初始化器使你的代码变得更加节制:
Project project = new Project(){
Name = "Schololarship Application Phase 1",
Description = "Create an application that allows student to apply for scholarship in the www.SampleSite.com web site.",
DateCreated = DateTime.Now.AddDays(-15),
StartDate = DateTime.Now.AddDays(-5),
DeadlineDate = DateTime.Now.AddDays(45),
Status = Status.In_Progress,
FixedFee = 40500.00m,
SpecialNotes = "This project has a firm deadline due to the fact that marketing information is already set to go out to advertize applying for scholarships online through the web site"
};