demand:
The display form can be a database, comprising form type, name, etc. in a dynamic interface, and must provide a new form is modified forms other functions.
In order to meet customers' changing needs, and sometimes need to increase as a commodity, modify, delete, attributes, so conventional database tables difficult to achieve,
Because the field is dead set table if you need to add a property when it is necessary to modify the table, I heard that this is not allowed ~~.
So we have to design a flexible database to computer equipment following example:
pc existing property name cpu ram disk Now we want to add a mainboard attribute the pc.
Now that must be provided to increase the form, then we create a table when he can not cpu ram disk for the PC table column names can only be modified if the value of
So it should establish a property sheet to save these values
Table y_property Create (
proid VARCHAR2 (16) Primary Key,
proname VARCHAR2 (64), - the attribute name
htmltype varchar2 (64), - the interface type
isneed number - if required
)
| proid | proname | htmltype | isneed |
| p001 | model | text | 0 |
| P002 | cpu | text | 0 |
| p003 | ram | select | 0 |
| p004 | disk | select | 0 |
Then to establish a value to a table to hold these computer attributes
create table y_provalues(
proid varchar2(32) , --属性id
entity varchar2(32) , --实例id
provalue varchar2(1024) ,--属性值
constraints pro_fk_proid foreign key (proid) references y_property(proid),
constraints provalues_pk primary key (proid,entity)
)
| proid | entity | provalue |
| p001 | e001 | Lenovo Yang days V45 |
| P002 | e001 | AMD5200 |
| p003 | e001 | Kingston |
| p004 | e001 | wd500g |
| p001 | E002 | HP450 |
| P002 | E002 | INTEL458 |
| p003 | E002 | Black Edition |
| p004 | E002 | wd320g |
In fact, it can be understood:
This table is a class y_property
This table is y_property y_provalues instance of this class. entity attribute is an instance number is the actual existence of a number of products.
In addition, we can also develop other tables make it more feature-rich on this basis of the above,
Such as computer-grade table, cpu table (so that we can associate with other tables y_provalues provalue in, the interface can provide drop-down list appears, select)
So down, then you can add attributes to a computer merchandise.
Transfer: http://yelifei94.iteye.com/blog/1041423
Personally, I feel there are several columns to achieve dynamic program for reference
It can be considered when creating a table, create more than a few reserved field
The DB table, adding columns sql = "alter tableName add columnName type (length)";
Reference: http://blog.csdn.net/casper_liu/article/details/1734989