Difference between revisions of "Database Metadata"

Revision as of 10:45, 19 July 2011

When you creates an extension is very common the need of a database to store data. You can create tables, but also need to create a bean with Hibernate XML mapping or annotations, a DAO, etc. The other way is creating meta-tables. These virtual tables are part of the OpenKM 5.1 Database Metadata feature. Let's see an example.

Our costumer want us to create a contact management. For this, we are going to create the metadata structure:

INSERT INTO OKM_DB_METADATA_TYPE (DMT_TABLE, DMT_REAL_COLUMN, DMT_TYPE, DMT_VIRTUAL_COLUMN) VALUES ('contact', 'col00', 'integer', 'con_id');
INSERT INTO OKM_DB_METADATA_TYPE (DMT_TABLE, DMT_REAL_COLUMN, DMT_TYPE, DMT_VIRTUAL_COLUMN) VALUES ('contact', 'col01', 'text', 'con_name');
INSERT INTO OKM_DB_METADATA_TYPE (DMT_TABLE, DMT_REAL_COLUMN, DMT_TYPE, DMT_VIRTUAL_COLUMN) VALUES ('contact', 'col02', 'text', 'con_mail');
INSERT INTO OKM_DB_METADATA_TYPE (DMT_TABLE, DMT_REAL_COLUMN, DMT_TYPE, DMT_VIRTUAL_COLUMN) VALUES ('contact', 'col03', 'text', 'con_phone');

In this sample, the meta-table "contact" contains 4 columns:

• COL 0 -> con_id
• COL 1 -> con_name
• COL 2 -> con_mail
• COL 3 -> con_phone

Actually a meta-table can contain no more than 15 columns.

An if you go to Administration -> Database Query you can see this new empty table:

Let's insert some data:

INSERT INTO OKM_DB_METADATA_VALUE (DMV_TABLE, DMV_COL00, DMV_COL01, DMV_COL02, DMV_COL03) VALUES ('contact', '1', 'Tai Lung', 'tlung@openkm.com', '555112233');
INSERT INTO OKM_DB_METADATA_VALUE (DMV_TABLE, DMV_COL00, DMV_COL01, DMV_COL02, DMV_COL03) VALUES ('contact', '2', 'Po Ping', 'pping@openkm.com', '555223344');
INSERT INTO OKM_DB_METADATA_VALUE (DMV_TABLE, DMV_COL00, DMV_COL01, DMV_COL02, DMV_COL03) VALUES ('contact', '3', 'Master Shifu', 'mshifu@openkm.com', '555334455');

This is the executed query again:

As you can see, now the inserted data is shown under its correct column. But this is not all, you can also filter these results using this syntax:

SELECT|contact|$con_name='Po Ping'

Which will display only results with virtual column "con_name" has the value "Po Ping". Not the $ symbol to refer to a virtual column. You can learn more on this in the next section.

Database Query syntax

The syntax used in the Database Query is defined as:

SENTENCE|TABLES|QUERY

Where TABLES is a list of meta-tables separated by a comma.

SELECT|TABLE
SELECT|TABLE|FILTER

where TABLE is an unique meta-table.

UPDATE|TABLE
UPDATE|TABLE|VALUES
UPDATE|TABLE|VALUES|FILTER

where TABLE is an unique meta-table.

DELETE|TABLE
DELETE|TABLE|FILTER

where TABLE is an unique meta-table.