使用复合设计模式对数据库进行mysql查询

Question

I'm not an SQL expert and therefore am having trouble wrapping my head around designing a mysql query to query database tables designed using the "composite design pattern."

The tables are:

composites: id, name, type [type is either "Condition" or "ConditionGroup"]

composites_properties: id, composite_id, property_id

groupings: id, parent_id, child_id

properties: id, key, value

What I want to do is generate a query that will return the unique properties of the group's ("ConditionGroup") member conditions ("Condition") such that I end up with a Group Name and a list of Property Keys (inherited from the member conditions).

The best I've come up with is:

SELECT DISTINCT properties.`key`, composites.name  
FROM composites, composites_properties, properties  
WHERE composites.id=composites_properties.composite_id
AND properties.id=composites_properties.property_id  
AND composites.id IN (
    SELECT child_id FROM groupings WHERE parent_id IN
        (SELECT id FROM composites WHERE type='ConditionGroup')
    )

This yields each member condition along with its list of properties where the properties are repeated if more than one member condition has that property.

In the end I'd like:

Group Name

• property_1

• property_2

• property_3

But I'm getting the following type list (with no indication to which group the conditions belong)

Condition Name 1 property_1

Condition Name 1 property_2

Condition Name 1 property_3

Condition Name 2 property_1

Condition Name 2 property_2

Condition Name 3 property_1

Condition Name 3 property_2

Any suggestions?

Answer 1

To be honest, I'm a little unclear on exactly what you are trying to accomplish, but I'll give it a shot. If you can clarify how this query does not do what you want, I can probably help further.

SELECT      c.name, p.key
FROM        composites c
INNER JOIN  groupings g ON c.id = g.parent_id
INNER JOIN  composites_properties cp ON cp.composite_id = g.child_id
INNER JOIN  properties p ON p.id = cp.property_id
WHERE       c.type = 'ConditionGroup'

This doesn't seem like the best query in the world to me because it ignores what the children in each grouping actually are, so I'm not sure this is what you want.