Grails - Find by non-native types

Question

I'm very new to grails (day 2).

First, I find it hard to find easily browsable resources (the documentation is very raw, and the tutorials are spread out and only show 'hello world' types of examples ).

I've set up my domain class with a relationship to other data types.

class ShopCategoryPage{
//some stuff
ProductProcedure procedure;
ProductCategory category;
//some stuff
}

In my controller, I am getting a category id and a procedure id as parameters, and I am trying to get the ShopCategoryPage associated with those parameters.

How do I "find" them? I tried passing the ids as procedureId or procedure_id, I tried passing a ProductProcedure object generated by findById ...

I'm not sure how to find by a property that is not of native type.

Answer 1

First, I find it hard to find easily browsable resources (the documentation is very raw, and the tutorials are spread out and only show 'hello world' types of examples ).

In my opinion the documentation is great, perhaps we're using different docs. I use:

• Grails Reference Documentation
• Grails JavaDoc
• GDK, i.e. methods Groovy adds to Java classes

If that still isn't satisfactory, I highly recommend the book "The Definitive Guide to Grails". I believe "Grails in Action" is also very good, but haven't read it. For learning Groovy, "Programming Groovy" is a great book (albeit a little out of date).

In my controller, I am getting a category id and a procedure id as parameters, and I am trying to get the ShopCategoryPage associated with those parameters.

The easiest way (though not the most efficient) is to use the dynamic finders.

// First of all load the ProductProcedure and ProductCategory 
// I'm assuming here the request params are named 'procedureId' and 'categoryId'
ProductProcedure productProcedure = ProductProcedure.get(params.procedureId.toLong())
ProductCategory productCategory = ProductCategory .get(params.categoryId.toLong())

// Now get the ShopCategoryPage associated with these. Replace 'find' with 'findAll'
// if there could be multiple associated ShopCategoryPages
ShopCategoryPage shopCategoryPage = ShopCategoryPage.findByProcedureAndCategory(productProcedure, productCategory)

A shortcoming of this approach is that it will cause 3 SELECT statements to be executed. If you're only interested in the shopCategoryPage returned by the last query, you could load this in "one shot" using HQL or a criteria query instead.

Answer 2

You should never use findById since it'll bypass the id-based 2nd-level cache and only use the query cache, which is a lot more volatile. Use get() instead.

Having said that, there's two ways to do this. One is to use get():

def shopCategoryPage = ShopCategoryPage.findByProcedureAndCategory(
       ProductProcedure.get(params.procedureId),
       ProductCategory.get(params.categoryId))

(use the appropriate param name for the two ids)

or using an HQL query (or a criteria query) to fetch the instance in one query instead of 3:

def shopCategoryPage = ShopCategoryPage.executeQuery(
   'from ShopCategoryPage p where p.procedure.id=:procedureId and p.category=:categoryId',
    [procedureId: params.procedureId.toLong(), categoryId: params.categoryId.toLong()])[0]

Answer 3

I agree, the easiest way is to use an dynamic finder.

In addition to 'The Definitive Guide to Grails' by Rocher and Brown, I suggest the IBM developerWorks track 'Mastering Grails' by Scott Davis.

http://www.ibm.com/developerworks/views/java/libraryview.jsp?site_id=1&contentarea_by=Java&sort_by=Date&sort_order=1&start=1&end=19&topic_by=&product_by=&type_by=All%20Types&show_abstract=true&search_by=mastering%20grails