c class relationships

Eloquent relationships Shorthand table there is a big pit in the Model association: When the Belongsto is reversed, the foreign key is automatically searched by the method name plus _id. In addition, the association is based on the model name plus _id as the foreign key. Type Define Inverse Remark One to one HasOne Belongsto Withdefault ()Define default foreign key→based on the model nameInverse defau

multiple a relationships.Advantages: It is more convenient to operate without having to build an intermediate table.Disadvantage: When the relationship between the two changes, it is not easy to maintain, and this association is one-way, that is, only suitable for one-way association. Scope of application Summary: associated with the enumeration table, associated with the attachment table, and other only one-way association, and the number of associations is not too many cases.Advantages: It is

Tags: span struct return over cannot call ONS testEmmm ... See the parent-child relationship directly by testing: class a{Constructor () {//does not have to This. Name= "Class_a"; //Console.log (This)//a {name: "Class_a"} (another line) B {name: "Class_a"}//the parent class subclasses performed a } static Staticcallnamea () {return"Name_a"; } Callnamea () {return"Name_a"; } static cover () {return"Cover_a"}} class B extends a{constructor () {//subclasses can not addSuper ();//subclasses

1. Many-to-many relationships and the realization of multi-state students, courses, teachers The relationship between the three is many-to-many, who shows the polymorphism of the class Model Layer Stu.rb Has_many:summaries Has_many:subjects,: Through =>:summaries,: Source =: Subject #实现多对多关系 Teacher.rb Has_many:summaries,:as =:p eople,:d ependent =:d Estroy #实现多态 Has_many:subjects,: Through =>:summaries,: Source =: Subject #实现多对多关系 Subject.rb Has_ma

the basis of the student table and curriculum, the school schedule is added to indicate the many-to-many relationship between students and the curriculum. The attributes that must be included in the selected schedule are the student number and the course number. (Student number, course number) This attribute set is just the keyword for choosing a timetable.code example:--Create student tablesCREATE TABLE Student (t_id INT PRIMARY KEY auto_increment,--School numberT_name VARCHAR (20),--Student n

Tags: RTC ons ati ICA nbsp set IPs val CodeOption Explicit Validationmode = True Interactivemode = Im_batch Dim MDL ' current model ' Get the current active model Set mdl = Activemodel If (MDL is Nothing) then MsgBox "There is no current Model" ElseIf not MDL. IsKindOf (Pdcdm.cls_model) Then ' if it's processing PDM, here's Pdpdm.cls_model MsgBox "The current model isn't an physical Data model." Else ProcessFolder MDL End If ' This routine copy name to comment for each table, each column and eac

not 0, no matter how to delete the file, the file is still strong!!! In general, the inode of the soft link and the source file is not related, soft link is a complete individual! A hard link does not cause the source file to be copied again, but all links to the same file are the same hard-link inode, and the size is the same. Because each hard-link inode is the same, it causes each hard link to be real deal associated with this source file! Postscript:The first time you write a blog, you s

record is the list of file names.R: Reads the list of directory structures. Like LS. Can see the file name, the properties of the files can not be seen, to see the file attributes also have the file's parent directory has the X permission.W: Modify the permissions of the directory structure list (and ignore the permissions of the list file). Include: Create new files, directories, delete files, directories, rename files, directories, move files, directories. For example, a normal user has a dir

= "JdbcTemplate")Private JdbcTemplate JdbcTemplate; @SuppressWarnings ("Unchecked")Public listString sql = "SELECT * from Cw_info where parent_id=" +CWID;if (ishidden==1) sql=sql+ "and is_hidden=" +ishidden;listfor (int i = 0; i listList.get (i). Setcwinfo (Cwlist);}return list;}@Override@SuppressWarnings ("Unchecked")Public listString sql = "SELECT * from Cw_info where parent_id=0";if (ishidden==1) sql=sql+ "and is_hidden=" +ishidden;listfor (int i = 0; i listCountlist.get (i). Setcwinfo (Cwlis

outside of the database table space it is located in? The answer is YES! It is perfectly possible to do so: then this is not a violation of the table belongs to the schema, and the schema belongs to the database, the database finally exists in the specified table space this network model?! Yes, it does seem counterintuitive, but it does make sense, and in reality, we often need to do this: table space on a slower disk for table data, and table space on a fast disk for the table's index. But we

In the object relationship model, we know there are three relationships: one-to-one, one-to-many, and many-to-many. This is only a conceptual relationship, but in a real relational database, we only have foreign keys, and there are no such three relationships, so let's talk about it in the relational database management system, how to implement these three relationships