Wednesday, September 06, 2006

sourceforge project

I just created a project on sourceforge:
http://sourceforge.net/projects/shadesdb

check it out!

6 comments:

  1. Anonymous12:05 PM

    setParam("FROM") and setPram("TO") for paging - do those actually get
    injected directly into sql? or are they some internal vars you set?

    ORMapping should probably support a dialect system like hibernate. it
    really
    sucks that it is part of the hierarchy now, because i like to develop
    on a
    different database then the one in prod, and it should be simple to
    swap.
    seems shades doesnt abstract as much of the db layer as
    hibernate/ejb3/whatever - i need to code to shades not to my underlying
    db
    imho.

    the dictionary can be improved by providing builders. new
    OneToManyBuilder(some params) that will build the string. less chances
    of
    typos.

    there needs to be a tool that will validate the dictionary against the
    current schema - prob by retrieving jdbc metadata. because a lot of
    things
    in the dict are defined by strings it would be great to know you didnt
    fat
    finger something on application startup rather then at some distant
    runtime.

    this definetely gives me the feeling of being much closer to the bare
    metal,
    which i think is nice if you want more control - and my favorite part
    is
    that you have to explicitly call update() to have your changes
    persisted :)

    on some high high level this reminds me of ibatis, but much more code
    centric.

    i really wish i had a project i could use this on right now to give you
    more
    valuable feedback, but i dont :(

    ReplyDelete
  2. "from" and "to" are just user-defined substitution variables in the query. SO the query was created like this, for example:

    RecordCandidate author = query.newCandidate(authorORM, "anAuthor");

    author.where("LIMIT ${from} OFFSET ${to}");

    You are right that shades queries are less portable than a JDOQL or dialect query, but the reason for that is flexibility. In shades, you can do absolutely anything that the underlying database supports.

    Good suggestion on the tool to check the schema. I have a schema generation tool, but what you suggested would be great.

    tell me more about your builder idea.

    Glad you like the explicit update method. This was a very intentional piece of the design.

    ReplyDelete
  3. Igor Vaynberg1:14 PM

    i understand the added flexibility for not making queries portable - but for me this would be a deal breaker. maybe build a system on top of shades that adds portability - but it would be much uglier and much more work for the end user.

    things that need to be portable are usually just identity generation and paging. i mean look here:

    http://josephlindsay.com/archives/2005/05/27/paging-results-in-ms-sql-server/

    users shouldnt have to build hacks like these themselves, and paging is different in almost every database.

    the builder i was talking about was for simple cases, so replace this

    dict.defineRelationship("student->teacher", "${this.alias}.FK = ${that.alias}.PK");

    with

    dict.defineRelations("student->teacher", FKBuilder.byPair("FK","PK"))

    for multi column fks you can do ManyToOne.byPair("FK1","PK1","FK2","PK2") and that would translate to ${this.alias}.FK1 = ${that.alias}.PK1 AND ${this.alias}.FK2 = ${that.alias}.PK2, just make it easier for 80% cases

    ReplyDelete
  4. Cool cool.

    I appreciate the feedback. Just so you know, the ORMapping does have all the capability to do initialization of columns on insert, identity generation, etc. For example DefaultHsqlORMapping extends DefaultORMapping and provides the proper identity generation for HSQLDB.

    But it very much is an intentional design choice to bring it a little closer to the metal. I appreciate the feedback.

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  5. Gwyn Evans2:25 PM

    It looks interesting, but I'd be afraid that it would only be useful for DB's that support a 'standard' SQL. Not that I know of any, though...! Specifically, for me, I'd want to know about Oracle support, as for paging, for instance, I needed to use the SQL format shown here... (http://www.wicket-wiki.org.uk/wiki/index.php/IBATIS#Oracle_paging).

    As Igor said, it's appears to be not too dissimilar in places to iBATIS, especially when using iBATIS's Abator tool to generate the QueryByExample code (e.g. http://ibatis.apache.org/docs/tools/abator/generatedobjects/exampleClassUsage.html#java2). I'm not suggesting you stop if it works for you but I am suggesting it might be an acceptable alternative for others to consider if the more esoteric DB behaviours do need too much special-coding...

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  6. Yeah, most paging SQL is not standard. I was considering adding an immutable query, that you could fully specify all the SQL for. Seems like I now have a good use case for that. Here is an example of using an immutable query for sorted pagination on Oracle. "immutable" just means that no alteration, aside from variable substitution, is made to the SQL you provide.

    String columns = myOrm.getColumns("STUDENT");
    String table = myORM.getTable();

    String sql = "SELECT * FROM( SELECT a.*, ROWNUM r FROM ( SELECT "+columns+" FROM "+table+" ORDER BY ${order-column}) a ) WHERE r BETWEEN ${start} AND ${end}";

    Query q = QueryFactory.newImmutableQuery(sql);
    q.candidate(studentORM);

    dbSess.setParameter("start","40");
    dbSess.setParameter("end","50");
    dbSess.setParameter("order-column", "LNAME");
    RecordSet rs = dbSess.executeQuery(conn,q)

    ReplyDelete