Grails findAll with sort, order, max and offset?

问题:

I want to integrate sort, order, max and offset in a findAll query. The following works fine:

def books = Book.findAll("from Book as b where b.approved=true order by b.dateCreated  desc", [max: max, offset: offset])

But what I want is:

def books = Book.findAll("from Book as b where b.approved=true", [sort: 'dateCreated', order: 'desc', max: max, offset: offset])

This does not work. How do I have to rewrite this?

回答1:

HQL doesn't support sort and order as parameters, so you need to include the "order by" as part of the HQL expression

def books = Book.findAll("from Book as b where b.approved=true"
  + " order by b.dateCreated desc", [max: max, offset: offset])

(or in this case just use Book.findAllByApproved(true, [...]) instead of HQL).

So if the sort and order are variables you need a trick like

def books = Book.findAll("from Book as b where b.approved=true"
  + (params.sort ? " order by b.${params.sort} ${params.order}" : ''), 
  [max: max, offset: offset])

回答2:

Using a where query works for me:

def books = Book.where{approved == true}.list(sort: 'dateCreated', order: 'desc', max: max, offset: offset)

Or with params straight from the page:

def books = Book.where{approved == true}.list(params)

回答3:

Using "findAllBy" because it supports sort and order.

def results = Book.findAllByTitle("The Shining",
             [max: 10, sort: "title", order: "desc", offset: 100])

Click here for details.

回答4:

I am assuming you are calling fetching the list of books in a controller or a service class.

If you are calling this from a controller action, then a magic variable "params" is already available to you. For example, if you request the page as follows

book/list?max=10&offset=2

then "params" will already have those values mapped automagically.

You can add more items to the params map as follows

params.sort = "dateCreated"
params.order = "desc"

Once you have build your params as desired, then you can use Grails dynamic query as follows

def books = Book.findAllByApproved(true, params)
// use "books" variable as you wish