Everyday Gaelyk: Save your query dsl for later use

21 březen 2013

In Gaelyk you can already save query created by query dsl using datastore.query{...} and than excute it using datastore prepare function but this method only support a subset of dsl statements - namely
select, from, where, and and sort. Corection using as or setting limit or offset is simply ignored.
In Gaelyk 2.0 you can use datastore.build{...} method
to create instance of QueryBuilder.

Warning! Thanks to Groovy 2.0 extension modules you can use helper method on any DatastoreService instance even outside groovlets or templates but you still have to assing the DatastoreService in datastore variable and call the methods on that variable to make query dsl transformation working.

This is current limitation and should change in time of final Gaelyk 2.0 release.

Let's show the difference between datastore.query and datastore.build methods:

Query method example

Query query = datastore.query {
    from 'Comment' as Comment
    where author == 10
    sort by crate desc
    limit 10        
}

PreparedQuery pq = datastore.prepare query

// The limit is gone! We need to set it again
FetchOptions.Builder options = withLimit(10)

// set the offset if there is page param specified
if(params.page){
    options = options.offset((params.page as int) * 10)
}

def comments = pq.asList(options.build())

// and we also get only entities not comments
for(Entity e in entity){
    // which needs to be coerced manually
    Comment comment = e as Comment
    process comment
}

When using datastore.query method a portion of query parameters where erased, expecially loosing coercion
is very confusing. On the other hand if you use datastore.build instead than all the information are kept.

Build method example

QueryBuiler dsl = datastore.build {
    from 'Comment' as Comment
    where author == 10
    sort by crate desc
    limit 10
}

// set the offset if there is page param specified
if(params.page){
    dsl.offset((params.page as int) * 10)
}

def comments = dsl.execute()

// no need to coerce manually
for(Comment in comments){
    process comment
}