many-to-many

问题 I'm an NHibernate developer trying to give Entity Framework a shot in a hobby project. I'm used to specifying mapping data in code using Fluent NHibernate. Pardoning Microsoft's belief that developers shouldn't be allowed to write code, I'm trying to create my mappings using the Entity Framework's visual designer surface (which you get by opening the .edmx file in Visual Studio). I have no idea how to set up a many-to-many relationship! I have 'updated the model' from the database, but I get

问题 I'm working with a legacy database where FK's aren't always used. For example I have an entity Person and an entity Country. A person has a Country which is mapped as a many-to-one in the Person mapping. <many-to-one name="Country" class="Country" foreign-key="none" lazy="false" not-found="ignore" fetch="join" outer-join="true" column="countryid"/> When person has null as column value (countryid) it won't perform an extra select query (because it knows that there won't be a reference in the

问题 I try to recuperate data from association ManyToMany but i can't, this is my code. Entity Produit : @Entity public class Produit implements Serializable { @Id @Column(name="Produit_ID") @GeneratedValue private Long id; private String dq; private String icForme; private String ich; private String icht; @ManyToMany(cascade = {CascadeType.ALL}) @JoinTable(name="produit_terminal", joinColumns={@JoinColumn(name="Produit_ID")}, inverseJoinColumns={@JoinColumn(name="Terminal_ID")}) private Set

问题 I have the below two classes: public class Project { public virtual int ProjectId { get; set; } public virtual string ProjectName { get; set; } public virtual LegalEntity LegalEntity { get; set; } } and public class LegalEntity { public virtual int LegalEntId { get; set; } public virtual string Name { get; set; } } with mappings as: <class name="Project" table="Project" dynamic-update="true"> <id name="ProjectId"> <generator class="native"/> </id> <property name="ProjectName" /> <many-to-one

问题 I have the following Many to many relationship (See the picture below) in my SQL server. In most cases there's are 2 rows in table tblWavelengths related to the table tblSensors, (in some cases only 1, and in extreme cases there can be 20 rows) I made the following simple query to retrieve the data from those 3 tables : select W.DateTimeID,S.SensorName,S.SensorType,W.Channel,W.PeakNr,W.Wavelength from tblWavelengths as W Left Join tblSensorWavelengths as SW on W.tblWavelengthID = SW

问题 What is the best way of handling many-to-many relations in a RDBMS database like mySQL? Have tried using a pivot table to keep track of the relationships, but it leads to either one of the following: Normalization gets left behind Columns that is empty or null What approach have you taken in order to support many-to-many relationships? 回答1: Keep track of a many-to-many relationship in a table specifically for that relationship (sometimes called a junction table ). This table models the

问题 I have the following scenario in my database. It is a record of Studies and those studies have other studies as prerequisites. In my DB design, it looks like this: And my code looks something like this: public class Study { public int ID { get; set; } public string Topic { get; set; } public byte TypeID { get; set; } public virtual StudyType Type { get; set; } public bool Deprecated { get; set; } public virtual ICollection<Study> Prerequisites { get; set; } } public class StudyType { public

问题 In trying to get a @OneToMany relationship between Article and HeaderField I probably have the mapping not quite right, resulting in: init: Deleting: /home/thufir/NetBeansProjects/USENET/build/built-jar.properties deps-jar: Updating property file: /home/thufir/NetBeansProjects/USENET/build/built-jar.properties compile: run: DEBUG: nntp: newsrc loading /home/thufir/.newsrc DEBUG: nntp: newsrc load: 1 groups in 31ms [EL Info]: 2012-07-31 02:05:05.677--ServerSession(8979162)--EclipseLink,

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 4 years ago . Is it possible to establish a Many-To-Many relationship between objects in Google App Engine? I am a newbie in GAE and still reading about it. The coding seems quite different from the usual Java coding I am used to. I've read the Getting Started guestbook tutorial. So, can I get any help/tutorials/videos

问题 Suppose I have 2 tables in a database. eg: Dog & Boss This is a many to many relationship, cause a boss can have more than 1 dog, and a dog can have more than 1 owner. I am the owner of Bobby, but so is my wife. But many to many is not allowed, so there is a helpertable: DogsPerBoss How to model this in code? Class Boss can have a collection of Dogs. Class Dog can have a collection of Bosses. --> at least, that is what I think. Perhaps there are better solutions? How about extra data that is