Question

I have a model whose rows I always want to sort based on the values in another associated model and I was thinking that the way to implement this would be to use set_dataset in the model. This is causing query results to be returned as hashes rather than objects, though, so none of the methods from the class can be used when iterating over the dataset.

I basically have two classes

class SortFields < Sequel::Model(:sort_fields)
    set_primary_key :objectid
end

class Items < Sequel::Model(:items)
    set_primary_key :objectid
    one_to_one :sort_fields, :class => SortFields, :key => :objectid
end

Some backstory: the data is imported from a legacy system into mysql. The values in sort_fields are calculated from multiple other associated tables (some one-to-many, some many-to-many) according to some complicated rules. The likely solution will be to just add the values in sort_fields to items (I want to keep the imported data separate from the calculated data, but I don’t have to). First, though, I just want to understand how far you can go with a dataset and still get objects rather than hashes.

If I set the dataset to sort on a field in items like so

class Items < Sequel::Model(:items)
    set_primary_key :objectid
    one_to_one :sort_fields, :class => SortFields, :key => :objectid
    set_dataset(order(:sortnumber))
end

then the expected clause is added to the generated SQL, e.g.:

>> Items.limit(1).sql
=> "SELECT * FROM `items` ORDER BY `sortnumber` LIMIT 1"

and queries still return objects:

>> Items.limit(1).first.class
=> Items

If I order it by the associated fields though…

class Items < Sequel::Model(:items)
    set_primary_key :objectid
    one_to_one :sort_fields, :class => SortFields, :key => :objectid
    set_dataset(
        eager_graph(:sort_fields).
        order(:sort1, :sort2, :sort3)
    )
end

…I get hashes

?> Items.limit(1).first.class
=> Hash

My first thought was that this happens because all fields from sort_fields are included in the results and maybe if selected only the fields from items I would get Items objects again:

class Items < Sequel::Model(:items)
    set_primary_key :objectid
    one_to_one :sort_fields, :class => SortFields, :key => :objectid
    set_dataset(
        eager_graph(:sort_fields).
        select(:items.*).
        order(:sort1, :sort2, :sort3)
    )
end

The generated SQL is what I would expect:

>> Items.limit(1).sql
=> "SELECT `items`.* FROM `items` LEFT OUTER JOIN `sort_fields` ON (`sort_fields`.`objectid` = `items`.`objectid`) ORDER BY `sort1`, `sort2`, `sort3` LIMIT 1"

It returns the same rows as the set_dataset(order(:sortnumber)) version but it still doesn’t work:

>> Items.limit(1).first.class
=> Hash

Before I add the sort fields to the items table so that they can all live happily in the same model, is there a way to tell Sequel to return on object when it wants to return a hash?

Answer 1

If you use #eager_graph, you must use #all instead of #each to retrieve the results in order for the graph to be processed (since you cannot eagerly load without having all instances up front), or use the eager_each plugin (which makes #each call #all internally).