53 lines
1.4 KiB
Ruby
53 lines
1.4 KiB
Ruby
# frozen_string_literal: true
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module Gitlab
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module SQL
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# Class for easily building CTE statements.
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#
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# Example:
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#
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# cte = CTE.new(:my_cte_name)
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# ns = Arel::Table.new(:namespaces)
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#
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# cte << Namespace.
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# where(ns[:parent_id].eq(some_namespace_id))
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#
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# Namespace
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# with(cte.to_arel).
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# from(cte.alias_to(ns))
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class CTE
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attr_reader :table, :query
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# name - The name of the CTE as a String or Symbol.
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def initialize(name, query)
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@table = Arel::Table.new(name)
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@query = query
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end
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# Returns the Arel relation for this CTE.
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def to_arel
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sql = Arel::Nodes::SqlLiteral.new("(#{query.to_sql})")
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Arel::Nodes::As.new(table, sql)
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end
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# Returns an "AS" statement that aliases the CTE name as the given table
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# name. This allows one to trick ActiveRecord into thinking it's selecting
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# from an actual table, when in reality it's selecting from a CTE.
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#
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# alias_table - The Arel table to use as the alias.
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def alias_to(alias_table)
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Arel::Nodes::As.new(table, alias_table)
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end
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# Applies the CTE to the given relation, returning a new one that will
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# query from it.
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def apply_to(relation)
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relation.except(:where)
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.with(to_arel)
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.from(alias_to(relation.model.arel_table))
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end
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end
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end
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end
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