Few questions about Grails' createCriteria

Question

I read about createCriteria, and kind of interested on how these works, and its usability in providing values for dropdown box.

So say, i have a table in the database, Resource table, where i have defined the table in the domain class called Resource.groovy. Resource table has a total of 10 columns, where 5 of it are

• Material Id
• Material description
• Resource
• Resource Id
• Product Code

So using the createCriteria, and i can use just like a query to return the items that i want to

def resList = Resource.createCriteria().list { 
        and { 
            eq('resource', resourceInstance)
            ne('materialId', '-')
        }
    }

Where in the above, i want to get the data that matches the resource = resourceInstance, and none of the materialId is equal to '-'.

I want to use the returned data from createCriteria above on my form, where i want to use some of the column on my select dropdown. Below is the code i used for my select dropdown.

<g:select id="resourceId" name="resourceId" 
                    from="${resList}"
                    disabled="${actionName != 'show' ? false : true}"  />

• How do i make it so that in a dropdown, it only shows the values taken from column Product Code? I believe the list created using createCriteria returns all 10 columns based on the createCriteria's specification. But i only want to use the Product Column values on my dropdown.
• How do i customize the data if in one of the select dropdown in my form, i wanted to show the values as "Resource Id - Resource Description"? The values are combination of more than 1 columns for one select dropdown but i don't know how to combine both in a single select dropdown.
• I read that hql and GORM query are better ways of fetching data from table than using createCriteria. Is this true?

Thanks

Answer 1

First of all refer to the document for using select in Grails. To answer all questions:

• Yes, the list to select from in the dropdown can be customized. In this case it should be something like from="${resList*.productCode}"

• Yes, this can be customized as well with something like

  from="${resList.collect { \"${it.resourceId} - ${it.resourceDesc}\" } }"

• It depends. If there are associations involved in a domain then using Criteria will lead to eager fetches which might not be required. But with HQL one gets the flexibility of tailoring the query as needed. With latest version of Grails those boundries are minimized a lot. Usage of DetachedCriteria, where queries etc are recommended whereever possible. So it is kind of mixing and matching to the scenario under consideration.