foreign-key-relationship

问题 I have two models like class Reporter(models.Model): first_name = models.CharField(max_length=30) last_name = models.CharField(max_length=30) email = models.EmailField() class Article(models.Model): headline = models.CharField(max_length=100) pub_date = models.DateField() reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE) Now for an object of Article lets say a=Article.objects.filter(id=1) a=a[0] I try to change the headline and the email of the author who has written this

问题 I have the following two classes, one ReqCandAssociation can have many Comments and it is mapped like so. I need to figure out a way that when I delete a ReqCandAssociation it deletes all of its associated comments. Thanks @Entity @Table(name = "candidate_jobReq") public class ReqCandAssociation implements Serializable { @Id private Integer candidateId; @Id private Integer jobId; @Column(name = "reqStatus") private String reqStatus; @ManyToOne @PrimaryKeyJoinColumn(name="candidateId",

问题 Currently developing an application using the newest version of symfony, obtained through PEAR. This is my exact schema configuration propel: user: id: name: { type: varchar(255), required: true } level: { type: integer, required: true, default: 1 } created_at: post: id: title: { type: varchar(255), required: true } post: { type: longvarchar, required: true } user_id: created_at: updated_at: comment: id: relation: integer comment: { type: varchar(300), required: true } nick: { type: varchar

问题 I was trying to create a table that has a one to many relationships. but it seems that adding a foreign key in Personal is not working. I am trying to link a Personal Information table to a address table? what is the solution for this error? Address table saved successfully Personal table Unable to create relationship 'FK_Personal_Address'. Cascading foreign key 'FK_Personal_Address' cannot be created where the referencing column 'Personal.ID' is an identity column. Could not create

问题 I am creating a database in MySQL for school. It has come up with the error 'cannot add foreign key constraint.' I have looked at other similar questions but cannot find out how it relates to my table. Please help! 回答1: Update your entries table like so: CREATE TABLE IF NOT EXISTS entries( entry_id INT UNSIGNED NOT NULL AUTO_INCREMENT, exam_date DATE NOT NULL, student_id INT REFERENCES students(student_id), subject_id INT REFERENCES subjects(subject_id), PRIMARY KEY(entry_id) ) 来源： https:/

问题 I am building a simple ASP.NET MVC app with Entity Framework Database First that allows a user to edit tables in a database. One table has a foreign key to another table. I want the user to be able to change the foreign key value. My question: How do I choose which column from the "foreign" table is displayed to the user in the view? I scaffolded the view out, but it is displaying the wrong column. The foreign key is in the DealerAuto table, which has columns: DealerAutoID, DealerID,

问题 i want to get the images form the image model in the template. class Products(models.Model): category = models.ForeignKey(Category) name= models.CharField(max_length=120, unique=True) slug = models.SlugField(unique = True) price = models.IntegerField(default=100) class Image(models.Model): property = models.ForeignKey(Products, related_name='images') image = models.ImageField(upload_to='static/images/home',blank=True,null=True) views.py def index(request): queryset = Products.objects.all()

问题 I'm working on a small blog engine. There are the following tables: Blog and Message. Blog has a foreign key: last_message_id, so I access the last message in the blog by calling blog.last_message I have the following code to make it work: class Blog < ActiveRecord::Base belongs_to :last_message, :class_name => "Message" end I need to order the blogs by the last messages. But when I call blogs.order("last_message.created_at DESC") It doesn't work. I get the following error: PGError: ERROR:

问题 What I am trying to is really quite straigh forward, but I cannot seem to get the mapping right with NHibernate. I am working up against a database with parent and child objects. The child objects have a foreign key reference to the primary key of the parent which is of datatype Guid. Pretty normal in any case. Now the database is set up in such a way that the foreign key field must never be null, so in case of orphan objects, with no parent, the foreign key should be an empty Guid ('00000000

问题 I'd like to have a principal entity ( Person ) with optional dependent entity ( Car ) mapped using the default conventions in Entity Framework code-first model. One solution is described in this answer, which uses the fluent API on modelBuilder to map to the key. Is it possible to do this using only the default EF conventions? The following code will throw a Unable to determine the principal end of an association between the types Person and Car. invalid operation exception. public