module Sequel::Model::Associations::DatasetMethods

  1. lib/sequel/model/associations.rb

Eager loading makes it so that you can load all associated records for a set of objects in a single query, instead of a separate query for each object.

Two separate implementations are provided. eager should be used most of the time, as it loads associated records using one query per association. However, it does not allow you the ability to filter or order based on columns in associated tables. eager_graph loads all records in a single query using JOINs, allowing you to filter or order based on columns in associated tables. However, eager_graph is usually slower than eager, especially if multiple one_to_many or many_to_many associations are joined.

You can cascade the eager loading (loading associations on associated objects) with no limit to the depth of the cascades. You do this by passing a hash to eager or eager_graph with the keys being associations of the current model and values being associations of the model associated with the current model via the key.

The arguments can be symbols or hashes with symbol keys (for cascaded eager loading). Examples:

Album.eager(:artist).all
Album.eager_graph(:artist).all
Album.eager(:artist, :genre).all
Album.eager_graph(:artist, :genre).all
Album.eager(:artist).eager(:genre).all
Album.eager_graph(:artist).eager_graph(:genre).all
Artist.eager(albums: :tracks).all
Artist.eager_graph(albums: :tracks).all
Artist.eager(albums: {tracks: :genre}).all
Artist.eager_graph(albums: {tracks: :genre}).all

You can also pass a callback as a hash value in order to customize the dataset being eager loaded at query time, analogous to the way the :eager_block association option allows you to customize it at association definition time. For example, if you wanted artists with their albums since 1990:

Artist.eager(albums: proc{|ds| ds.where{year > 1990}})

Or if you needed albums and their artist’s name only, using a single query:

Albums.eager_graph(artist: proc{|ds| ds.select(:name)})

To cascade eager loading while using a callback, you substitute the cascaded associations with a single entry hash that has the proc callback as the key and the cascaded associations as the value. This will load artists with their albums since 1990, and also the tracks on those albums and the genre for those tracks:

Artist.eager(albums: {proc{|ds| ds.where{year > 1990}}=>{tracks: :genre}})

Public Instance methods

as_hash(key_column=nil, value_column=nil, opts=OPTS)

If the dataset is being eagerly loaded, default to calling all instead of each.

[show source]
     # File lib/sequel/model/associations.rb
3299 def as_hash(key_column=nil, value_column=nil, opts=OPTS)
3300   if (@opts[:eager_graph] || @opts[:eager]) && !opts.has_key?(:all)
3301     opts = Hash[opts]
3302     opts[:all] = true
3303   end
3304   super
3305 end
association_join(*associations)

Adds one or more INNER JOINs to the existing dataset using the keys and conditions specified by the given association(s). Take the same arguments as eager_graph, and operates similarly, but only adds the joins as opposed to making the other changes (such as adding selected columns and setting up eager loading).

The following methods also exist for specifying a different type of JOIN:

association_full_join

FULL JOIN

association_inner_join

INNER JOIN

association_left_join

LEFT JOIN

association_right_join

RIGHT JOIN

Examples:

# For each album, association_join load the artist
Album.association_join(:artist).all
# SELECT *
# FROM albums
# INNER JOIN artists AS artist ON (artists.id = albums.artist_id)

# For each album, association_join load the artist, using a specified alias
Album.association_join(Sequel[:artist].as(:a)).all
# SELECT *
# FROM albums
# INNER JOIN artists AS a ON (a.id = albums.artist_id)

# For each album, association_join load the artist and genre
Album.association_join(:artist, :genre).all
Album.association_join(:artist).association_join(:genre).all
# SELECT *
# FROM albums
# INNER JOIN artists AS artist ON (artist.id = albums.artist_id)
# INNER JOIN genres AS genre ON (genre.id = albums.genre_id)

# For each artist, association_join load albums and tracks for each album
Artist.association_join(albums: :tracks).all
# SELECT *
# FROM artists
# INNER JOIN albums ON (albums.artist_id = artists.id)
# INNER JOIN tracks ON (tracks.album_id = albums.id)

# For each artist, association_join load albums, tracks for each album, and genre for each track
Artist.association_join(albums: {tracks: :genre}).all
# SELECT *
# FROM artists
# INNER JOIN albums ON (albums.artist_id = artists.id)
# INNER JOIN tracks ON (tracks.album_id = albums.id)
# INNER JOIN genres AS genre ON (genre.id = tracks.genre_id)

# For each artist, association_join load albums with year > 1990
Artist.association_join(albums: proc{|ds| ds.where{year > 1990}}).all
# SELECT *
# FROM artists
# INNER JOIN (
#   SELECT * FROM albums WHERE (year > 1990)
# ) AS albums ON (albums.artist_id = artists.id)

# For each artist, association_join load albums and tracks 1-10 for each album
Artist.association_join(albums: {tracks: proc{|ds| ds.where(number: 1..10)}}).all
# SELECT *
# FROM artists
# INNER JOIN albums ON (albums.artist_id = artists.id)
# INNER JOIN (
#   SELECT * FROM tracks WHERE ((number >= 1) AND (number <= 10))
# ) AS tracks ON (tracks.albums_id = albums.id)

# For each artist, association_join load albums with year > 1990, and tracks for those albums
Artist.association_join(albums: {proc{|ds| ds.where{year > 1990}}=>:tracks}).all
# SELECT *
# FROM artists
# INNER JOIN (
#   SELECT * FROM albums WHERE (year > 1990)
# ) AS albums ON (albums.artist_id = artists.id)
# INNER JOIN tracks ON (tracks.album_id = albums.id)
[show source]
     # File lib/sequel/model/associations.rb
3005 def association_join(*associations)
3006   association_inner_join(*associations)
3007 end
complex_expression_sql_append(sql, op, args)

If the expression is in the form x = y where y is a Sequel::Model instance, array of Sequel::Model instances, or a Sequel::Model dataset, assume x is an association symbol and look up the association reflection via the dataset’s model. From there, return the appropriate SQL based on the type of association and the values of the foreign/primary keys of y. For most association types, this is a simple transformation, but for many_to_many associations this creates a subquery to the join table.

[show source]
     # File lib/sequel/model/associations.rb
3016 def complex_expression_sql_append(sql, op, args)
3017   r = args[1]
3018   if (((op == :'=' || op == :'!=') && r.is_a?(Sequel::Model)) ||
3019       (multiple = ((op == :IN || op == :'NOT IN') && ((is_ds = r.is_a?(Sequel::Dataset)) || (r.respond_to?(:all?) && r.all?{|x| x.is_a?(Sequel::Model)})))))
3020     l = args[0]
3021     if ar = model.association_reflections[l]
3022       raise Error, "filtering by associations is not allowed for #{ar.inspect}" if ar[:allow_filtering_by] == false
3023 
3024       if multiple
3025         klass = ar.associated_class
3026         if is_ds
3027           if r.respond_to?(:model)
3028             unless r.model <= klass
3029               # A dataset for a different model class, could be a valid regular query
3030               return super
3031             end
3032           else
3033             # Not a model dataset, could be a valid regular query
3034             return super
3035           end
3036         else
3037           unless r.all?{|x| x.is_a?(klass)}
3038             raise Sequel::Error, "invalid association class for one object for association #{l.inspect} used in dataset filter for model #{model.inspect}, expected class #{klass.inspect}"
3039           end
3040         end
3041       elsif !r.is_a?(ar.associated_class)
3042         raise Sequel::Error, "invalid association class #{r.class.inspect} for association #{l.inspect} used in dataset filter for model #{model.inspect}, expected class #{ar.associated_class.inspect}"
3043       end
3044 
3045       if exp = association_filter_expression(op, ar, r)
3046         literal_append(sql, exp)
3047       else
3048         raise Sequel::Error, "invalid association type #{ar[:type].inspect} for association #{l.inspect} used in dataset filter for model #{model.inspect}"
3049       end
3050     elsif multiple && (is_ds || r.empty?)
3051       # Not a query designed for this support, could be a valid regular query
3052       super
3053     else
3054       raise Sequel::Error, "invalid association #{l.inspect} used in dataset filter for model #{model.inspect}"
3055     end
3056   else
3057     super
3058   end
3059 end
eager(*associations)

The preferred eager loading method. Loads all associated records using one query for each association.

The basic idea for how it works is that the dataset is first loaded normally. Then it goes through all associations that have been specified via eager. It loads each of those associations separately, then associates them back to the original dataset via primary/foreign keys. Due to the necessity of all objects being present, you need to use all to use eager loading, as it can’t work with each.

This implementation avoids the complexity of extracting an object graph out of a single dataset, by building the object graph out of multiple datasets, one for each association. By using a separate dataset for each association, it avoids problems such as aliasing conflicts and creating cartesian product result sets if multiple one_to_many or many_to_many eager associations are requested.

One limitation of using this method is that you cannot filter the current dataset based on values of columns in an associated table, since the associations are loaded in separate queries. To do that you need to load all associations in the same query, and extract an object graph from the results of that query. If you need to filter based on columns in associated tables, look at eager_graph or join the tables you need to filter on manually.

Each association’s order, if defined, is respected. If the association uses a block or has an :eager_block argument, it is used.

To modify the associated dataset that will be used for the eager load, you should use a hash for the association, with the key being the association name symbol, and the value being a callable object that is called with the associated dataset and should return a modified dataset. If that association also has dependent associations, instead of a callable object, use a hash with the callable object being the key, and the dependent association(s) as the value.

Examples:

# For each album, eager load the artist
Album.eager(:artist).all
# SELECT * FROM albums
# SELECT * FROM artists WHERE (id IN (...))

# For each album, eager load the artist and genre
Album.eager(:artist, :genre).all
Album.eager(:artist).eager(:genre).all
# SELECT * FROM albums
# SELECT * FROM artists WHERE (id IN (...))
# SELECT * FROM genres WHERE (id IN (...))

# For each artist, eager load albums and tracks for each album
Artist.eager(albums: :tracks).all
# SELECT * FROM artists
# SELECT * FROM albums WHERE (artist_id IN (...))
# SELECT * FROM tracks WHERE (album_id IN (...))

# For each artist, eager load albums, tracks for each album, and genre for each track
Artist.eager(albums: {tracks: :genre}).all
# SELECT * FROM artists
# SELECT * FROM albums WHERE (artist_id IN (...))
# SELECT * FROM tracks WHERE (album_id IN (...))
# SELECT * FROM genre WHERE (id IN (...))

# For each artist, eager load albums with year > 1990
Artist.eager(albums: proc{|ds| ds.where{year > 1990}}).all
# SELECT * FROM artists
# SELECT * FROM albums WHERE ((year > 1990) AND (artist_id IN (...)))

# For each artist, eager load albums and tracks 1-10 for each album
Artist.eager(albums: {tracks: proc{|ds| ds.where(number: 1..10)}}).all
# SELECT * FROM artists
# SELECT * FROM albums WHERE (artist_id IN (...))
# SELECT * FROM tracks WHERE ((number >= 1) AND (number <= 10) AND (album_id IN (...)))

# For each artist, eager load albums with year > 1990, and tracks for those albums
Artist.eager(albums: {proc{|ds| ds.where{year > 1990}}=>:tracks}).all
# SELECT * FROM artists
# SELECT * FROM albums WHERE ((year > 1990) AND (artist_id IN (...)))
# SELECT * FROM albums WHERE (artist_id IN (...))
[show source]
     # File lib/sequel/model/associations.rb
3136 def eager(*associations)
3137   opts = @opts[:eager]
3138   association_opts = eager_options_for_associations(associations)
3139   opts = opts ? opts.merge(association_opts) : association_opts
3140   clone(:eager=>opts.freeze)
3141 end
eager_graph(*associations)

The secondary eager loading method. Loads all associations in a single query. This method should only be used if you need to filter or order based on columns in associated tables, or if you have done comparative benchmarking and determined it is faster.

This method uses Dataset#graph to create appropriate aliases for columns in all the tables. Then it uses the graph’s metadata to build the associations from the single hash, and finally replaces the array of hashes with an array model objects inside all.

Be very careful when using this with multiple one_to_many or many_to_many associations, as you can create large cartesian products. If you must graph multiple one_to_many and many_to_many associations, make sure your filters are narrow if the datasets are large.

Each association’s order, if defined, is respected. eager_graph probably won’t work correctly on a limited dataset, unless you are only graphing many_to_one, one_to_one, and one_through_one associations.

Does not use the block defined for the association, since it does a single query for all objects. You can use the :graph_* association options to modify the SQL query.

Like eager, you need to call all on the dataset for the eager loading to work. If you just call each, it will yield plain hashes, each containing all columns from all the tables.

To modify the associated dataset that will be joined to the current dataset, you should use a hash for the association, with the key being the association name symbol, and the value being a callable object that is called with the associated dataset and should return a modified dataset. If that association also has dependent associations, instead of a callable object, use a hash with the callable object being the key, and the dependent association(s) as the value.

You can specify an custom alias and/or join type on a per-association basis by providing an Sequel::SQL::AliasedExpression object instead of an a Symbol for the association name.

You cannot mix calls to eager_graph and graph on the same dataset.

Examples:

# For each album, eager_graph load the artist
Album.eager_graph(:artist).all
# SELECT ...
# FROM albums
# LEFT OUTER JOIN artists AS artist ON (artists.id = albums.artist_id)

# For each album, eager_graph load the artist, using a specified alias
Album.eager_graph(Sequel[:artist].as(:a)).all
# SELECT ...
# FROM albums
# LEFT OUTER JOIN artists AS a ON (a.id = albums.artist_id)

# For each album, eager_graph load the artist, using a specified alias
# and custom join type

Album.eager_graph(Sequel[:artist].as(:a, join_type: :inner)).all
# SELECT ...
# FROM albums
# INNER JOIN artists AS a ON (a.id = albums.artist_id)

# For each album, eager_graph load the artist and genre
Album.eager_graph(:artist, :genre).all
Album.eager_graph(:artist).eager_graph(:genre).all
# SELECT ...
# FROM albums
# LEFT OUTER JOIN artists AS artist ON (artist.id = albums.artist_id)
# LEFT OUTER JOIN genres AS genre ON (genre.id = albums.genre_id)

# For each artist, eager_graph load albums and tracks for each album
Artist.eager_graph(albums: :tracks).all
# SELECT ...
# FROM artists
# LEFT OUTER JOIN albums ON (albums.artist_id = artists.id)
# LEFT OUTER JOIN tracks ON (tracks.album_id = albums.id)

# For each artist, eager_graph load albums, tracks for each album, and genre for each track
Artist.eager_graph(albums: {tracks: :genre}).all
# SELECT ...
# FROM artists
# LEFT OUTER JOIN albums ON (albums.artist_id = artists.id)
# LEFT OUTER JOIN tracks ON (tracks.album_id = albums.id)
# LEFT OUTER JOIN genres AS genre ON (genre.id = tracks.genre_id)

# For each artist, eager_graph load albums with year > 1990
Artist.eager_graph(albums: proc{|ds| ds.where{year > 1990}}).all
# SELECT ...
# FROM artists
# LEFT OUTER JOIN (
#   SELECT * FROM albums WHERE (year > 1990)
# ) AS albums ON (albums.artist_id = artists.id)

# For each artist, eager_graph load albums and tracks 1-10 for each album
Artist.eager_graph(albums: {tracks: proc{|ds| ds.where(number: 1..10)}}).all
# SELECT ...
# FROM artists
# LEFT OUTER JOIN albums ON (albums.artist_id = artists.id)
# LEFT OUTER JOIN (
#   SELECT * FROM tracks WHERE ((number >= 1) AND (number <= 10))
# ) AS tracks ON (tracks.albums_id = albums.id)

# For each artist, eager_graph load albums with year > 1990, and tracks for those albums
Artist.eager_graph(albums: {proc{|ds| ds.where{year > 1990}}=>:tracks}).all
# SELECT ...
# FROM artists
# LEFT OUTER JOIN (
#   SELECT * FROM albums WHERE (year > 1990)
# ) AS albums ON (albums.artist_id = artists.id)
# LEFT OUTER JOIN tracks ON (tracks.album_id = albums.id)
[show source]
     # File lib/sequel/model/associations.rb
3246 def eager_graph(*associations)
3247   eager_graph_with_options(associations)
3248 end
eager_graph_with_options(associations, opts=OPTS)

Run eager_graph with some options specific to just this call. Unlike eager_graph, this takes the associations as a single argument instead of multiple arguments.

Options:

:join_type

Override the join type specified in the association

:limit_strategy

Use a strategy for handling limits on associations. Appropriate :limit_strategy values are:

true

Pick the most appropriate based on what the database supports

:distinct_on

Force use of DISTINCT ON stategy (*_one associations only)

:correlated_subquery

Force use of correlated subquery strategy (one_to_* associations only)

:window_function

Force use of window function strategy

:ruby

Don’t modify the SQL, implement limits/offsets with array slicing

This can also be a hash with association name symbol keys and one of the above values, to use different strategies per association.

The default is the :ruby strategy. Choosing a different strategy can make your code significantly slower in some cases (perhaps even the majority of cases), so you should only use this if you have benchmarked that it is faster for your use cases.

[show source]
     # File lib/sequel/model/associations.rb
3270 def eager_graph_with_options(associations, opts=OPTS)
3271   return self if associations.empty?
3272 
3273   opts = opts.dup unless opts.frozen?
3274   associations = [associations] unless associations.is_a?(Array)
3275   ds = if eg = @opts[:eager_graph]
3276     eg = eg.dup
3277     [:requirements, :reflections, :reciprocals, :limits].each{|k| eg[k] = eg[k].dup}
3278     eg[:local] = opts
3279     ds = clone(:eager_graph=>eg)
3280     ds.eager_graph_associations(ds, model, ds.opts[:eager_graph][:master], [], *associations)
3281   else
3282     # Each of the following have a symbol key for the table alias, with the following values:
3283     # :reciprocals :: the reciprocal value to use for this association
3284     # :reflections :: AssociationReflection instance related to this association
3285     # :requirements :: array of requirements for this association
3286     # :limits :: Any limit/offset array slicing that need to be handled in ruby land after loading
3287     opts = {:requirements=>{}, :master=>alias_symbol(first_source), :reflections=>{}, :reciprocals=>{}, :limits=>{}, :local=>opts, :cartesian_product_number=>0, :row_proc=>row_proc}
3288     ds = clone(:eager_graph=>opts)
3289     ds = ds.eager_graph_associations(ds, model, ds.opts[:eager_graph][:master], [], *associations).naked
3290   end
3291 
3292   ds.opts[:eager_graph].freeze
3293   ds.opts[:eager_graph].each_value{|v| v.freeze if v.is_a?(Hash)}
3294   ds
3295 end
to_hash_groups(key_column, value_column=nil, opts=OPTS)

If the dataset is being eagerly loaded, default to calling all instead of each.

[show source]
     # File lib/sequel/model/associations.rb
3309 def to_hash_groups(key_column, value_column=nil, opts=OPTS)
3310   if (@opts[:eager_graph] || @opts[:eager]) && !opts.has_key?(:all)
3311     opts = Hash[opts]
3312     opts[:all] = true
3313   end
3314   super
3315 end
ungraphed()

Do not attempt to split the result set into associations, just return results as simple objects. This is useful if you want to use eager_graph as a shortcut to have all of the joins and aliasing set up, but want to do something else with the dataset.

[show source]
     # File lib/sequel/model/associations.rb
3321 def ungraphed
3322   ds = super.clone(:eager_graph=>nil)
3323   if (eg = @opts[:eager_graph]) && (rp = eg[:row_proc])
3324     ds = ds.with_row_proc(rp)
3325   end
3326   ds
3327 end

Protected Instance methods

eager_graph_association(ds, model, ta, requirements, r, *associations)

Call graph on the association with the correct arguments, update the eager_graph data structure, and recurse into eager_graph_associations if there are any passed in associations (which would be dependencies of the current association)

Arguments:

ds

Current dataset

model

Current Model

ta

table_alias used for the parent association

requirements

an array, used as a stack for requirements

r

association reflection for the current association, or an SQL::AliasedExpression with the reflection as the expression, the alias base as the alias (or nil to use the default alias), and an optional hash with a :join_type entry as the columns to use a custom join type.

*associations

any associations dependent on this one

[show source]
     # File lib/sequel/model/associations.rb
3346 def eager_graph_association(ds, model, ta, requirements, r, *associations)
3347   if r.is_a?(SQL::AliasedExpression)
3348     alias_base = r.alias
3349     if r.columns.is_a?(Hash)
3350       join_type = r.columns[:join_type]
3351     end
3352     r = r.expression
3353   else
3354     alias_base = r[:graph_alias_base]
3355   end
3356   assoc_table_alias = ds.unused_table_alias(alias_base)
3357   loader = r[:eager_grapher]
3358   if !associations.empty?
3359     if associations.first.respond_to?(:call)
3360       callback = associations.first
3361       associations = {}
3362     elsif associations.length == 1 && (assocs = associations.first).is_a?(Hash) && assocs.length == 1 && (pr_assoc = assocs.to_a.first) && pr_assoc.first.respond_to?(:call)
3363       callback, assoc = pr_assoc
3364       associations = assoc.is_a?(Array) ? assoc : [assoc]
3365     end
3366   end
3367   local_opts = ds.opts[:eager_graph][:local]
3368   limit_strategy = r.eager_graph_limit_strategy(local_opts[:limit_strategy])
3369 
3370   if r[:conditions] && !Sequel.condition_specifier?(r[:conditions]) && !r[:orig_opts].has_key?(:graph_conditions) && !r[:orig_opts].has_key?(:graph_only_conditions) && !r.has_key?(:graph_block)
3371     raise Error, "Cannot eager_graph association when :conditions specified and not a hash or an array of pairs.  Specify :graph_conditions, :graph_only_conditions, or :graph_block for the association.  Model: #{r[:model]}, association: #{r[:name]}"
3372   end
3373 
3374   ds = loader.call(:self=>ds, :table_alias=>assoc_table_alias, :implicit_qualifier=>(ta == ds.opts[:eager_graph][:master]) ? first_source : qualifier_from_alias_symbol(ta, first_source), :callback=>callback, :join_type=>join_type || local_opts[:join_type], :join_only=>local_opts[:join_only], :limit_strategy=>limit_strategy, :from_self_alias=>ds.opts[:eager_graph][:master])
3375   if r[:order_eager_graph] && (order = r.fetch(:graph_order, r[:order]))
3376     ds = ds.order_append(*qualified_expression(order, assoc_table_alias))
3377   end
3378   eager_graph = ds.opts[:eager_graph]
3379   eager_graph[:requirements][assoc_table_alias] = requirements.dup
3380   eager_graph[:reflections][assoc_table_alias] = r
3381   if limit_strategy == :ruby
3382     eager_graph[:limits][assoc_table_alias] = r.limit_and_offset 
3383   end
3384   eager_graph[:cartesian_product_number] += r[:cartesian_product_number] || 2
3385   ds = ds.eager_graph_associations(ds, r.associated_class, assoc_table_alias, requirements + [assoc_table_alias], *associations) unless associations.empty?
3386   ds
3387 end
eager_graph_associations(ds, model, ta, requirements, *associations)

Check the associations are valid for the given model. Call eager_graph_association on each association.

Arguments:

ds

Current dataset

model

Current Model

ta

table_alias used for the parent association

requirements

an array, used as a stack for requirements

*associations

the associations to add to the graph

[show source]
     # File lib/sequel/model/associations.rb
3398 def eager_graph_associations(ds, model, ta, requirements, *associations)
3399   associations.flatten.each do |association|
3400     ds = case association
3401     when Symbol, SQL::AliasedExpression
3402       ds.eager_graph_association(ds, model, ta, requirements, eager_graph_check_association(model, association))
3403     when Hash
3404       association.each do |assoc, assoc_assocs|
3405         ds = ds.eager_graph_association(ds, model, ta, requirements, eager_graph_check_association(model, assoc), assoc_assocs)
3406       end
3407       ds
3408     else
3409       raise(Sequel::Error, 'Associations must be in the form of a symbol or hash')
3410     end
3411   end
3412   ds
3413 end
eager_graph_build_associations(hashes)

Replace the array of plain hashes with an array of model objects will all eager_graphed associations set in the associations cache for each object.

[show source]
     # File lib/sequel/model/associations.rb
3417 def eager_graph_build_associations(hashes)
3418   hashes.replace(_eager_graph_build_associations(hashes, eager_graph_loader))
3419 end