Class: Sequel::Dataset::PlaceholderLiteralizer
- Defined in:
- lib/sequel/dataset/placeholder_literalizer.rb
Overview
PlaceholderLiteralizer allows you to record the application of arbitrary changes to a dataset with placeholder arguments, recording where those placeholder arguments are used in the query. When running the query, the literalization process is much faster as Sequel can skip most of the work it normal has to do when literalizing a dataset.
Basically, this enables optimizations that allow Sequel to cache the SQL produced for a given dataset, so that it doesn’t need to recompute that information every time.
Example:
loader = Sequel::Dataset::PlaceholderLiteralizer.loader(DB[:items]) do |pl, ds|
ds.where(:id=>pl.arg).exclude(:name=>pl.arg).limit(1)
end
loader.first(1, "foo")
# SELECT * FROM items WHERE ((id = 1) AND (name != 'foo')) LIMIT 1
loader.first(2, "bar")
# SELECT * FROM items WHERE ((id = 2) AND (name != 'bar')) LIMIT 1
Caveats:
Note that this method does not handle all possible cases. For example:
loader = Sequel::Dataset::PlaceholderLiteralizer.loader(DB[:items]) do |pl, ds|
ds.join(pl.arg, :item_id=>:id)
end
loader(:cart_items)
Will not qualify the item_id column with cart_items. In this type of situation it’s best to add a table alias when joining:
loader = Sequel::Dataset::PlaceholderLiteralizer.loader(DB[:items]) do |pl, ds|
ds.join(Sequel.as(pl.arg, :t), :item_id=>:id)
end
loader(:cart_items)
There are other similar cases that are not handled, mainly when Sequel changes the SQL produced depending on the types of the arguments.
Defined Under Namespace
Class Method Summary collapse
-
.loader(dataset, &block) ⇒ Object
Create a PlaceholderLiteralizer by yielding a Recorder and dataset to the given block, recording the offsets at which the recorders arguments are used in the query.
Instance Method Summary collapse
-
#all(*args, &block) ⇒ Object
Return an array of all objects by running the SQL query for the given arguments.
-
#each(*args, &block) ⇒ Object
Run the SQL query for the given arguments, yielding each returned row to the block.
-
#first(*args) ⇒ Object
Run the SQL query for the given arguments, returning the first row.
-
#get(*args) ⇒ Object
Run the SQL query for the given arguments, returning the first value.
-
#initialize(dataset, fragments, final_sql, arity) ⇒ PlaceholderLiteralizer
constructor
Save the dataset, array of SQL fragments, and ending SQL string.
-
#sql(*args) ⇒ Object
Return the SQL query to use for the given arguments.
Constructor Details
#initialize(dataset, fragments, final_sql, arity) ⇒ PlaceholderLiteralizer
Save the dataset, array of SQL fragments, and ending SQL string.
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# File 'lib/sequel/dataset/placeholder_literalizer.rb', line 117 def initialize(dataset, fragments, final_sql, arity) @dataset = dataset @fragments = fragments @final_sql = final_sql @arity = arity end |
Class Method Details
.loader(dataset, &block) ⇒ Object
Create a PlaceholderLiteralizer by yielding a Recorder and dataset to the given block, recording the offsets at which the recorders arguments are used in the query.
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# File 'lib/sequel/dataset/placeholder_literalizer.rb', line 112 def self.loader(dataset, &block) Recorder.new.loader(dataset, &block) end |
Instance Method Details
#all(*args, &block) ⇒ Object
Return an array of all objects by running the SQL query for the given arguments. If a block is given, yields all objects to the block after loading them.
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# File 'lib/sequel/dataset/placeholder_literalizer.rb', line 126 def all(*args, &block) @dataset.with_sql_all(sql(*args), &block) end |
#each(*args, &block) ⇒ Object
Run the SQL query for the given arguments, yielding each returned row to the block.
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# File 'lib/sequel/dataset/placeholder_literalizer.rb', line 131 def each(*args, &block) @dataset.with_sql_each(sql(*args), &block) end |
#first(*args) ⇒ Object
Run the SQL query for the given arguments, returning the first row.
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# File 'lib/sequel/dataset/placeholder_literalizer.rb', line 136 def first(*args) @dataset.with_sql_first(sql(*args)) end |
#get(*args) ⇒ Object
Run the SQL query for the given arguments, returning the first value. For this to make sense, the dataset should return a single row with a single value (or no rows).
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# File 'lib/sequel/dataset/placeholder_literalizer.rb', line 142 def get(*args) @dataset.with_sql_single_value(sql(*args)) end |
#sql(*args) ⇒ Object
Return the SQL query to use for the given arguments.
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# File 'lib/sequel/dataset/placeholder_literalizer.rb', line 147 def sql(*args) raise Error, "wrong number of arguments (#{args.length} for #{@arity})" unless args.length == @arity s = '' ds = @dataset @fragments.each do |sql, i, transformer| s << sql v = args.fetch(i) v = transformer.call(v) if transformer ds.literal_append(s, v) end if sql = @final_sql s << sql end s end |