EAV模型是Zend框架的基础,而Magento项目又是建立在Zend框架的基础上的,所有了解EAV有助于了解Magento的架构原理,在开发Magento相关应用时非常有用。
EAV:Entity-Attribute-Value的缩写,是数据库模型的一种,使用eav建模的好处是可以动态为数据模型增加或移除属性。

1. 问题提出:
假设需要定义一个实体Customer的信息,通常我们只要定义一个表为customer,并定义相应的属性即可。倘若某天需要为customer增加一个新的属性如“爱好”,那么就需要更改表的结构。
如果使用EAV模型则不必改变表结构。

2. Magento的EAV模型定义:

在Magento中,EAV模型相关的表定义有:
eav_attribute            
eav_attribute_group      
eav_attribute_option     
eav_attribute_option_value
eav_attribute_set        
eav_entity               
eav_entity_attribute     
eav_entity_datetime      
eav_entity_decimal       
eav_entity_int           
eav_entity_store         
eav_entity_text          
eav_entity_type          
eav_entity_varchar

现在让我来观察最重要的三张表
eav_entity_type,eav_entity_attribute,eav_attribute

1) eav_entity_type表用来定义实体的基本信息。

mysql>  select  *  from   eav_entity_type  where  entity_type_id=1; 
+----------------+------------------+-------------------+-----------------+-----------------+
| entity_type_id | entity_type_code | entity_model      | attribute_model | entity_table    |
+----------------+------------------+-------------------+-----------------+-----------------+
|              1 | customer         | customer/customer |                 | customer/entity | 
+----------------+------------------+-------------------+-----------------+-----------------+  

2). eav_entity_attribute表用来定义实体customer模型包含哪些属性

mysql>  select  *  from  eav_entity_attribute   where  entity_type_id= '1' ; 
+---------------------+----------------+------------------+--------------------+--------------+
| entity_attribute_id | entity_type_id | attribute_set_id | attribute_group_id | attribute_id | 
+---------------------+----------------+------------------+--------------------+--------------+
|                   1 |              1 |                1 |                  1 |            1 | 
|                   2 |              1 |                1 |                  1 |            2 | 
|                   3 |              1 |                1 |                  1 |            3 | 
|                   4 |              1 |                1 |                  1 |            4 | 
|                   5 |              1 |                1 |                  1 |            5 | 
|                   6 |              1 |                1 |                  1 |            6 | 
|                   7 |              1 |                1 |                  1 |            7 | 
|                   8 |              1 |                1 |                  1 |            8 | 
|                   9 |              1 |                1 |                  1 |            9 | 
|                  10 |              1 |                1 |                  1 |           10 | 
|                  11 |              1 |                1 |                  1 |           11 | 
|                  12 |              1 |                1 |                  1 |           12 | 
|                  13 |              1 |                1 |                  1 |           13 | 
|                  14 |              1 |                1 |                  1 |           14 | 
|                  15 |              1 |                1 |                  1 |           15 | 
|                  16 |              1 |                1 |                  1 |           16 | 
+---------------------+----------------+------------------+--------------------+--------------+ 

3), 由上表推出customer实体包含16个属性,下面的语句查看每个属性的具体定义
 
mysql>  select  *  from  eav_attribute  where  attribute_id<=16  and  attribute_id>=1 ; 
+--------------+----------------+------------------+---------------+  
| attribute_id | entity_type_id | attribute_code   | backend_type  | 
+--------------+----------------+------------------+---------------+  
|            1 |              1 | website_id       | static        | 
|            2 |              1 | store_id         | static        | 
|            3 |              1 | created_in       | varchar       | 
|            4 |              1 | prefix           | varchar       | 
|            5 |              1 | firstname        | varchar       | 
|            6 |              1 | middlename       | varchar       | 
|            7 |              1 | lastname         | varchar       | 
|            8 |              1 | suffix           | varchar       | 
|            9 |              1 | email            | static        | 
|           10 |              1 | group_id         | static        | 
|           11 |              1 | dob              | datetime      | 
|           12 |              1 | password_hash    | varchar       | 
|           13 |              1 | default_billing  | int           | 
|           14 |              1 | default_shipping | int           | 
|           15 |              1 | taxvat           | varchar       | 
|           16 |              1 | confirmation     | varchar       | 
+--------------+----------------+------------------+---------------+  
所以,使用上述的模型,一旦有CUSTOMER属性定义的添加和删除,只需要增加或删除 eav_entity_attribute的记录即可

3. 使用EAV模型
现在,在Magento系统注册一个新的用户,看看实例数据如何存放在数据库
 
mysql>  select  *  from  customer_entity            ; 
+-----------+----------------+------------------+------------+--------------------+  
| entity_id | entity_type_id | attribute_set_id | website_id | email              | 
+-----------+----------------+------------------+------------+--------------------+  
|         1 |              1 |                0 |          1 | xxx@gmail.com
+-----------+----------------+------------------+------------+--------------------+  
 
mysql> select  *  from  customer_entity_varchar    ; 
+----------+----------------+--------------+-----------+-------------------------------------+
| value_id | entity_type_id | attribute_id | entity_id | value                               | 
+----------+----------------+--------------+-----------+-------------------------------------+
|        1 |              1 |            5 |         1 | Koda                                | 
|        2 |              1 |            7 |         1 | Guo                                 | 
|        4 |              1 |            3 |         1 | Default  Store  View                | 
|        5 |              1 |           12 |         1 | 2256e441b74ab3454a41c821f5de1e9d:9s | 
+----------+----------------+--------------+-----------+-------------------------------------+
从上表看到customer_entity 和customer_entity_varchar用来存放相应属性的实际输入值。如:
Koda, Guo分别属性编号5,7即firstname和lastname实际值

和customer实体定义相对应的实例存放的相关表包括:
 
customer_entity           
customer_entity_datetime  
customer_entity_decimal   
customer_entity_int       
customer_entity_text      
customer_entity_varchar   

总 结:
了解Magento的EAV模型结构是扩展Magento必须的知识。 其意义在于,我们常常需要扩展Magento某些实体的属性,或者创建自定义的eav模型实例。希望本文对你有所启示。