64 lines
1.8 KiB
Ruby
64 lines
1.8 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 recursive CTE statements.
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#
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# Example:
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#
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# cte = RecursiveCTE.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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# cte << Namespace.
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# from([ns, cte.table]).
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# where(ns[:parent_id].eq(cte.table[:id]))
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#
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# Namespace.with.
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# recursive(cte.to_arel).
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# from(cte.alias_to(ns))
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class RecursiveCTE
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attr_reader :table
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# name - The name of the CTE as a String or Symbol.
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def initialize(name)
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@table = Arel::Table.new(name)
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@queries = []
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end
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# Adds a query to the body of the CTE.
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#
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# relation - The relation object to add to the body of the CTE.
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def <<(relation)
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@queries << relation
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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(Union.new(@queries).to_sql)
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Arel::Nodes::As.new(table, Arel::Nodes::Grouping.new(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
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.recursive(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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