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From Thomas Fischer <tfisc...@apache.org>
Subject Interface for Criteria and Criteria.Criterion
Date Sat, 28 Jan 2006 10:53:36 GMT
This is continuing the discussion I had with Greg Monroe on creating an 
interface to access Criteria and Criteria.Criterion from the other
Torque classes. See
http://issues.apache.org/scarab/issues/id/TRQS341
for Greg's suggestion and previous discussion

> IMHO, it is a good idea to have a well define interfaces (or an abstract 
> class) between major areas of responsiblity. In the long run, this helps 
> keep the areas from stepping on each other and helps in testing, 
> debugging, and enhancing the areas separate from each other.

This is certainly a good point, I agree to that. But now it comes to what 
areas of responsibilities we want to define by the interfaces you 
suggested. I can see two main ideas in your CriteriaInterface. The first 
is "1) A provider of information for composing an SQL Query", the second 
is "2) An object defining the contents of an SQL insert/update/delete". 
Here are the methods that do not fit into 1):

CriteriaInterface.getNewCriterion(), CriteriaInterface.setLimit(), 
CriteriaInterface.setOffset(), CriteriaInterface.remove(), 
CriteriaInterface.add(), CriteriaInterface.addSelectColumn()

The setLimit() and setOffset() methods are only used by LargeSelect(), 
they also do not fit into the pattern 2).

Then there are methods which are just convenience methods:

CriteriaInterface.getColumnName(), CriteriaInterface.getComparison(), 
CriteriaInterface.getTableName(),CriteriaInterface.getValue()

The methods

CriteriaInterface.getFloat(), CriteriaInterface.getDouble()...

are both convenience methods and are an overshot at the only place they
are used (VillageUtils.setVillageValue), a simple cast would be enough
there.

Then, there are methods you have marked yourself as deprecated and are not 
used anymore:

CriteriaInterface.getJoinL(), CriteriaInterface.getJoinR()

The equals() method is defined by any java Object and does not need to be 
included in an interface declaration.

And, to make the list complete, including something I have said before: 
The "extends Map" in the CriteriaInterface exposes an implementation 
detail and should be avoided (I do hope we do not use it anywhere).

So my suggestion would be to split the CriteriaInterface in two 
interfaces: QueryDataProvider(used for selects and deletes) and 
UpdateDataProvider(used for updates and inserts), and remove the methods I 
have mentioned above which are cluttering up the interface. The idea 
between splitting is that we would have reasonably small interfaces with 
well defined uses. Also, we would be to be able to use a separate object 
for updates/inserts at some point.

If this seems reasonable, then we would also have to create two Criterion 
Interfaces: QueryDataConstraint and UpdateDataElement.

The Criterion Interface has more methods which are needed by other Torque 
classes but do not fit into the above pattern. This is because the 
Criterion still renders itself in SQL. If this is factored out (as was 
already done in the Criteria class), these methods can be removed. My
suggestion would be to move the SQL rendering code to 
the SQLBuilder class.

Because this would also affect the interface to be created, I would 
suggest to make Criterion a static inner class of Criteria. The reference 
from Criterion to its enclosing Criterion object is that it uses the 
Criteria's DB object, and as a default of the ignoreCase setting if no 
specific ignoreCase is set for the criterion. Both is only neede for SQL 
rendering, and could be accessed there by providing the enclosing Criteria 
as additional argument.

In my opinion, Greg's suggestion plus the changes outlined above would 
clear up the internal structure of the Criteria mechanism a lot. Any 
opinions ?

     Thomas

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