我需要在数据库的2个表中插入一行。这两个表之间的关系是一对多。这是他们的模型：
NSUInteger width, height, i;
CGContextRef context;
void *data;
CGColorSpaceRef colorSpace;
UIFont *font;
font = [UIFont fontWithName:name size:size];
width = (NSUInteger)dimensions.width;
if ((width != 1) && (width & (width - 1))) {
i = 1;
while (i < width)
i *= 2;
width = i;
}
height = (NSUInteger)dimensions.height;
if ((height != 1) && (height & (height - 1))) {
i = 1;
while (i < height)
i *= 2;
height = i;
}
colorSpace = CGColorSpaceCreateDeviceGray();
data = calloc(height, width);
context = CGBitmapContextCreate(data, width, height, 8, width, colorSpace, kCGImageAlphaNone);
CGColorSpaceRelease(colorSpace);
CGContextSetGrayFillColor(context, 1.0, 1.0);
CGContextTranslateCTM(context, 0.0, height);
CGContextScaleCTM(context, 1.0f, -1.0f); //NOTE: NSString draws in UIKit referential i.e. renders upside-down compared to CGBitmapContext referential
UIGraphicsPushContext(context);
NSMutableParagraphStyle *style = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
[style setLineBreakMode:NSLineBreakByWordWrapping];
NSDictionary *attrsDictionary = @{
NSFontAttributeName: font,
NSBaselineOffsetAttributeName: @1.0F,
NSParagraphStyleAttributeName: style
};
[string drawInRect:CGRectMake(0, 0, dimensions.width, dimensions.height)
withAttributes:attrsDictionary];
UIGraphicsPopContext();
// Here I use "void *data" to obtain an OpenGL texture
// ...
// ...
CGContextRelease(context);
free(data);
这是上下文：
public partial class Task
{
public Task()
{
TaskOwner = new HashSet<TaskOwner>();
}
public int Id { get; set; }
public string Action { get; set; }
public int ActualEffort { get; set; }
public DateTime AssignationDate { get; set; }
public int EstEffort { get; set; }
public DateTime EstEnd { get; set; }
public bool IsComplete { get; set; }
public int ProjectId { get; set; }
public string Status { get; set; }
public virtual ICollection<TaskOwner> TaskOwner { get; set; }
public virtual Project Project { get; set; }
}
public partial class TaskOwner
{
public int Id { get; set; }
public int EmployeId { get; set; }
public int TaskId { get; set; }
public virtual Employe Employe { get; set; }
public virtual Task Task { get; set; }
}
一个任务可以由多个TaskOwner拥有。我试过这个approch：
modelBuilder.Entity<Task>(entity =>
{
entity.HasIndex(e => e.ProjectId)
.HasName("FKTask25514");
entity.Property(e => e.Id)
.HasColumnName("id")
.HasColumnType("int(10)");
entity.Property(e => e.Action)
.IsRequired()
.HasColumnName("action")
.HasColumnType("varchar(255)");
entity.Property(e => e.ActualEffort)
.HasColumnName("actual_effort")
.HasColumnType("int(10)");
entity.Property(e => e.AssignationDate).HasColumnName("assignation_date");
entity.Property(e => e.EstEffort)
.HasColumnName("est_effort")
.HasColumnType("int(10)");
entity.Property(e => e.EstEnd).HasColumnName("est_end");
entity.Property(e => e.IsComplete).HasColumnType("tinyint(1)");
entity.Property(e => e.ProjectId)
.HasColumnName("project_id")
.HasColumnType("int(10)");
entity.Property(e => e.Status)
.IsRequired()
.HasColumnName("status")
.HasColumnType("varchar(255)");
entity.HasOne(d => d.Project)
.WithMany(p => p.Task)
.HasForeignKey(d => d.ProjectId)
.OnDelete(DeleteBehavior.Restrict)
.HasConstraintName("FKTask25514");
});
modelBuilder.Entity<TaskOwner>(entity =>
{
entity.ToTable("Task_Owner");
entity.HasIndex(e => e.EmployeId)
.HasName("FKTask_Owner320287");
entity.HasIndex(e => e.TaskId)
.HasName("FKTask_Owner395416");
entity.Property(e => e.Id)
.HasColumnName("id")
.HasColumnType("int(10)");
entity.Property(e => e.EmployeId)
.HasColumnName("employe_id")
.HasColumnType("int(10)");
entity.Property(e => e.TaskId)
.HasColumnName("task_id")
.HasColumnType("int(10)");
entity.HasOne(d => d.Employe)
.WithMany(p => p.TaskOwner)
.HasForeignKey(d => d.EmployeId)
.OnDelete(DeleteBehavior.Restrict)
.HasConstraintName("FKTask_Owner320287");
entity.HasOne(d => d.Task)
.WithMany(p => p.TaskOwner)
.HasForeignKey(d => d.TaskId)
.OnDelete(DeleteBehavior.Restrict)
.HasConstraintName("FKTask_Owner395416");
});
然后将其保存到数据库中，但我总是解除此错误：
使用“Models.TaskOwner”类型检测到自引用循环。 Path'[6] .taskOwner [0] .employe.taskOwner'。
如果可以的话，我会使用我刚创建的任务的id并将其链接到taskOwner模型，但由于id是自动生成的，我不能或者至少我不知道如何。我究竟做错了什么？做我想要完成的事情的正确方法是什么？
答案 0 :(得分：1)
因此Task有零个或多个TaskOwners。每个TaskOwner只有一个Task。没有TaskOwners没有Task。
这意味着，如果数据库中存在TaskOwner，则不能拥有第二个Task。但是，你可以让它拥有一个不同的Task而不是它现在拥有的{。}}。
如果向数据库中引入（添加）与数据库中现有对象关系的对象，则可以使用相关对象的Id或对象本身（当然，它具有非零值） ID）。
如果相关对象也是新对象，只需将相关对象分配给要添加的对象即可。您不必单独添加相关对象。
请注意，只要您没有使用SaveChanges，就不能使用任何新对象的ID。
介绍一个拥有现有任务和现有员工的TaskOwner
using (var dbContext = new MyDbContext())
{
int employeeId = FetchEmployeeId(...);
int taskId = FetchTaskId(...);
TaskOwner introducedTaskOwner = dbContext.TaskOwners.Add(new TaskOwner()
{
// don't fill the ID!
EmployeeId = employeeId,
TaskId = taskId,
... // other properties
});
dbContext.SaveChanges();
// now the introduced task owner has an Id!
return introducedTaskOwner;
}
将TaskOwner与新任务一起引入。使用现有员工
现在你无法填写TaskId，而是填写任务：
using (var dbContext = new MyDbContext())
{
int employeeId = FetchEmployeeId(...);
TaskOwner introducedTaskOwner = dbContext.TaskOwners.Add(new TaskOwner()
{
// don't fill the TaskOwner ID!
EmployeeId = employeeId,
// Give the Task owner a non-existing Task:
Task = new Task()
{
// don't fill the Task ID!
// don't fill the collection of TaskOwners
... // fill other Task properties
}
... // other task owner properties
});
dbContext.SaveChanges();
// now both the task owner and the task are introduced. Both have an ID
Debug.Assert(introducedTaskOwner.Id != 0);
Debug.Assert(intrducedTaskOwner.TaskId != 0);
Debug.Assert(introducedTaskOwner.Task.Id != 0);
}
如果你想要，你可以先介绍Task，然后再介绍TaskOwner。只要您没有使用SaveChanges，就不能使用任何Id。
using (var dbContext = new MyDbContext())
{
int employeeId = FetchEmployeeId(...);
Task introducedTask = dbContext.Tasks.Add(new Task()
{
// don't fill the Task ID!
TaskOwners = new List<TaskOwner>(); // This Task has no owners yet
... // fill other Task properties
});
TaskOwner introducedTaskOwner = dbContext.TaskOwners.Add(new TaskOwner()
{
// don't fill the TaskOwner ID!
EmployeeId = employeeId,
// Give the Task owner a the introduced task
Task = introducedTask,
... // other task owner properties
});
dbContext.SaveChanges();
}
您也可以反过来执行此操作：您可以将TaskOwner添加到现有（或新添加的）任务
using (var dbContext = new MyDbContext())
{
int employeeId = FetchEmployeeId(...);
// get existing task:
Task existingTask = dbContext.Tasks
.Where(task => task.ActualEffort > ...)
.OrderBy(task => task.ActualEffort)
.FirstOrDefault();
// add an owner to the task owners collection:
existingTask.TaskOwners.Add(new TaskOwner()
{
// don't fill the TaskOwner ID!
EmployeeId = employeeId,
// no need to fill the TaskId, nor the Task
// Entity Framework knows the Task to which it belongs, because you
// add it to the TaskOwners collection
...
});
dbContext.SaveChanges();
}
结论：只要您没有Id，请使用完整对象。如果尚未添加对象，实体框架将添加它
答案 1 :(得分：0)
首先，您需要保存Models.Task并访问自动生成的ID，然后保存TaskOwner模型。