one-to-many

My question is close to this one , but does not exactly fit with mine. I've this column in an entity: /** * @var ArrayCollection[SubjectTag] * * @ORM\OneToMany(targetEntity="SubjectTag", mappedBy="subject") * @Assert\Count(max = 10, maxMessage = "You can't create more than 10 tags.") * @Assert\Valid() */ protected $subjectTags; I want to dynamically order my tags by a position, defined in SubjectTag.position . Try using the doctrine2 ORM functionality for Ordering To-Many Associations like this: /** * @var ArrayCollection[SubjectTag] * * @ORM\OneToMany(targetEntity="SubjectTag", mappedBy=

I'm hoping I'm just doing something silly here... I'm trying to set up JPA annotations for a Map<String, Phone> and getting the following stack trace. Exception [EclipseLink-6069] (Eclipse Persistence Services - 2.4.1.v20121003-ad44345): org.eclipse.persistence.exceptions.QueryException Exception Description: The field [EMPLOYEE.PHONE_TYPE] in this expression has an invalid table in this context. Query: ReadAllQuery(name="phones" referenceClass=Phone ) at org.eclipse.persistence.exceptions.QueryException.invalidTableForFieldInExpression(QueryException.java:739) at org.eclipse.persistence

This question is based on the thread . If we have one-to-many data structure, we need to have a "help-table" to store for instance phonenumbers for one person. Many person cannot have the same phonenumbers. I look forward for an explanation why we then need two "help-tables" between many-to-many relations. An example of this is a question-site where many users can add the same tags: alt text http://files.getdropbox.com/u/175564/db/db-55.png Why do we need to have the tables Question-Tag-xref and Question-Tags ? Why cannot we just have one table for tags as follows? Question_id | tag 1 C 1 C++

I have an object in C# like this: private ClassWidget { public int ID; public List<int> WidgetFavoriteNumbers; } Let's say I have two tables in SQL, one defines widget properties, and the other holds many records for a single widget, let's say the widget's favorite numbers: widgets ----------- id (int, not null) // other properties ... widget_nums ---------- widget_id (int, not null) num (int) I find myself frequently executing two SQL queries to populate this object even though I know I can join the tables to create just one query. The reason is that it seems simpler to populate the object

I have the data model you can see below, and a nested SUBQUERY predicate, but in somehow it just not works. Any idea how to correct it? I figured out, this here down is working finally: [NSPredicate predicateWithFormat:@"SUBQUERY(bs, $B, SUBQUERY($B.cs, $C, $C.ds.name != \"xxx\").@count > 0).@count > 0"]; Ok, so here is the working solution: [NSPredicate predicateWithFormat:@"SUBQUERY(bs, $B, SUBQUERY($B.cs, $C, $C.ds.name != \"xxx\").@count > 0).@count > 0"]; 来源： https://stackoverflow.com/questions/13242383/what-is-wrong-in-my-nested-subquery-predicate

I am trying to create a one-to-many relationship using Flask and SQLAlchemy. I want the one-to-many relationship to be as so: "For any single movie, there can be multiple characters" Here it what I have so far, but it is saving in my DB as one-to-one right now. (One movie to one character, saving multiple times in DB for multiple characters) class Movie(db.Model): __tablename__ = "movies" id = db.Column('movies_id', db.Integer, primary_key=True) movie_type = db.Column('movie_type', db.Text()) def __init__(self, movie_type): self.movie_type = movie_type def __repr__(self): return '<Movie %r>' %