mybatis learning framework - multi-table query

La Riba winded

The multi-table queries mybatis 
    relationships between tables There are several: 
        many 
        many-to- 
        one- 
        to-many 
    examples: 
        the user and the order is many 
        orders and many-user is 
            a user can place multiple orders 
            multiple orders belong to the same user 

        and the ID number is the one 
            a person can have only one ID number 
            an ID card number can only belong to one person 

        is many to many between teacher and student 
            a student teacher may be more I taught 
            a student teacher can pay more 
    exception: 
        if out each order, he can only belong to one user. 
        So Mybatis put many to look into one. 
    
    The multi-table queries mybatis: 
        Example: the user account and 
            a user may have multiple accounts 
            an account can only belong to one user (s account may also belong to the same user) 
        Step: 
            1 , the establishment of two tables: a user table, account table
                So that users have a one to many relationship between the table and the account table: 
                the need to add foreign key in the account Table 
            2 , the establishment of two entity classes: classes and user entities account entity classes 
                allows users to type and entity accounts can be reflected a the relationship between the number of 
            3 , the establishment of two profiles 
                the user's profile 
                account profile 
            4 , for configuration: 
                when we query the user, the user can obtain account information contained in the same time 
                when we check your account, you can get an account at the same time user information belongs 

        example: users and roles 
            a user can have multiple roles 
            a role can give multiple users 
        steps: 
            1 , the establishment of two tables: a user table, table role 
                allows users and role tables have a many to many relationship. 
                Need to use an intermediate table, the intermediate table comprising a respective main key, in the middle of the table is a foreign key. 
            2 , create two entity classes: class of user entities and roles entity classes 
                allow the user entity classes and roles can be reflected many relationships 
                each other contains a collection of reference
            3 , the establishment of two profiles 
                profile user 
                role profiles 
            4 , for configuration: 
                When we query the user, the user can get character information contained while 
                the user when we query role, the role can be simultaneously conferred information