Hibernate basic Mapping

with the step-by-step practice of hibernate , it is necessary to make a summary, so that you can make your ideas clearer!

I. Knowledge generalization

The whole idea of mind mapping is:

second, the corresponding structure diagram and implementation     Span lang= "ZH-CN" style= "Font-family:calibri" >   (i) One-way, single-connection mapping ( one-to-one ):

A pair of relationships between two objects, for example: person (people)-idcard (ID)

There are two strategies that can be implemented for a-to-one correlation mapping:

         * PRIMARY Key Association: that is, let two objects have the same primary key value to indicate a one by one corresponding relationship between them; database tables do not have additional fields to maintain relationships between them, and are only associated with the primary key of the table. such as:

Example: one-way primary Key Association example connection

         * Unique Foreign Key association: A Foreign Key association, originally used for many-to-one configurations, but with a unique limit ( <many-to-one> label to map, specify a multiple end Unique to be true , which limits the multiplicity of one end to the other, and can also be used to denote a single-to-one correlation, in fact it is a multi-pair special case. such as:

Example: one-way, single-click, unique Foreign Key Association example connection

Note: Because a one-to-one primary key correlation mapping is not good enough, when our needs change to become one-to-many, it becomes impossible to operate, so when we encounter a one-to-one correlation, we often use unique foreign key associations to solve the problem, rarely using a one-to-one primary key association.

(b) One-way many-to-one correlation mapping (many-to-one):

Many-to-one correlation mapping principle: Add a foreign key at one end of the many, point to the end of a, such as:

Key Mapping code--Add the following tag mappings at one end of the number:

<span style= "FONT-SIZE:18PX;" >[java] viewplaincopy01.<many-to-onename= "group" column= "GroupID"/>  </span>

(iii) unidirectional one-to-many association mappings (one-to-many):

One-to-many correlation mappings and many-to-one correlation mappings are consistent, with a foreign key at one end, pointing to the end of the other . such as (Students and classes):

Note: The difference between it and many-to-one is that the maintenance relationship is different

        * Many-to-one maintenance relationship is: a multi-point relationship, with this relationship, when loading can be loaded up

        * A one -to-many maintenance relationship is: a point-to-many relationship, with this relationship, when loading one can be more loaded up

Key Mapping code--Add the following tag mappings at one end:

<span style= "FONT-SIZE:18PX;" >[java] viewplaincopy01.<setname= "Students" >.      <keycolumn= "Classesid"/>.      <one-to-manyclass= "Com.hibernate.Student"/> 04.</set> </span>

      defect: Because one end of the manyStudentDon't knowClassesthe existence (i.e.StudentNo maintenance andClassesthe relationship) so in the SaveStudentWhen the relationship fieldClassesidis forNULL, If the relationship field is set to non-empty, the data cannot be saved, and the common workaround is to use bidirectional associative mappings instead, see6.

(d) One-way many-to-many mappings (Many-to-many):

Many-to-many association mappings add a new table to complete the basic mapping, such as:

Key Mapping code--You can Add the following tag mappings at one end of the User:

<span style= "FONT-SIZE:18PX;" >[java] viewplaincopy01.<setname= "Roles" table= "T_user_role" >.     <keycolumn= "user_id"/>.     <many-to-manyclass= "Com.hibernate.Role" column= "role_id"/> 04.</set> </span>

(v ) bidirectional one-to-one correlation mapping:

In contrast to one-way mapping, it is necessary to add <one-to-one> tags to the idcard , it does not affect, only affects loading. such as:

bidirectional one-to-one primary key Mapping key mapping code- Add the following tag mappings on the Idcard side:

<span style= "FONT-SIZE:18PX;" >[java] viewplaincopy01.<one-to-onename= "person"/> </span>

bidirectional one-to-one one-to-one unique foreign key mapping code--Add the following tag mappings on the Idcard side:

<span style= "FONT-SIZE:18PX;" >[java] viewplaincopy01.<one-to-onename= "person" property-ref= "Idcard"/> </span>

Note: one-to-one unique Foreign Key Association bidirectional adoption <one-to-one> tag mapping, must be specified <one-to-one> The Property-ref property in the label is the name of the relationship field

(vi ) bidirectional one-to-many association mappings (very Important):

The purpose of using a one-to-many bidirectional association mapping is primarily to solve the problem of a pair of multi-directional associations rather than demand-driven.

A one-to-many bidirectional association mapping method:

              * at one end of the set, using the <key> tags, adding a foreign key to the multiple end

              * at one end of the multi-use <many-to-one> label

Note:the<key> tag and <many-to-one> tag fields remain constant, otherwise data clutter

Key Mapping code:

Add the following tag mappings at one end of the Classes :

<span style= "FONT-SIZE:18PX;" >[java] viewplaincopy01.<setname= "Students" inverse= "true" >.       <keycolumn= "Classesid"/>.      <one-to-manyclass= "Com.hibernate.Student"/> 04.</set>      Add the following tag mappings at one end of the Student: [Java] Viewplaincopy01 . <many-to-onename= "Classes" column= "Classesid"/> </span>

Comment:inverse Property

                * Inverse property can be used on a one-to-many and many-to-many bidirectional association, inverse . Span lang= "en-US" style= "Font-family:simsun" the property defaults to false inverse true

* Inverse is the reversal in the control direction, affecting only the storage

(vii) bidirectional Many-to-many association mappings:

Two-way purpose is to both sides can be loaded up, and one-way many-to-many difference is two-way need to add tag mapping at both ends, it should be noted that:

              * The resulting intermediate table name must be the same

              * The fields in the resulting intermediate table must be the same

Role (role) side key mapping code:

<span style= "FONT-SIZE:18PX;" >[java] viewplaincopy01.<setname= "users" table= "T_user_role" >.       <keycolumn= "role_id"/>.       <many-to-manyclass= "Com.hibernate.User" column= "user_id"/> 04.lt;/set>        user-side key mapping code:        [Java] Viewplaincopy01.<setname= "Roles" table= "T_user_role" >.      <keycolumn= "user_id"/>.      <many-to-many class= "Com.hibernate.Role" column= "role_id"/> 04.lt;/set> </span>

Iii. Summary

for the above basic mapping relationship summary and application in the project, let me feel in real life often have such demand, so we must master and learn skillfully!

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Hibernate basic Mapping