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A toolkit for data mapping and language integrated query for Elixir
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lib/ecto/repo/assoc.ex
defmodule Ecto.Repo.Assoc do
# The module invoked by repomodules
# for association related functionality.
@moduledoc false
@doc """
Transforms a result set based on query assocs, loading
the associations onto their parent model.
"""
@spec query([Ecto.Model.t], Ecto.Query.t) :: [Ecto.Model.t]
def query(rows, query)
def query([], _query), do: []
def query(rows, %{assocs: []}), do: rows
def query(rows, %{assocs: assocs, sources: sources}) do
# Pre-create rose tree of reflections and accumulator
# dicts in the same structure as the fields tree
refls = create_refls(0, assocs, sources)
accs = create_accs(assocs)
# Replace the dict in the accumulator by a list
# We use it as a flag to store the substructs
accs = put_elem(accs, 1, [])
# Populate tree of dicts of associated entities from the result set
{_keys, rows, sub_dicts} = Enum.reduce(rows, accs, fn row, acc ->
merge(row, acc, 0) |> elem(0)
end)
# Retrieve and load the assocs from cached dictionaries recursively
for {item, sub_structs} <- Enum.reverse(rows) do
[load_assocs(item, sub_dicts, refls)|sub_structs]
end
end
defp merge([struct|sub_structs], {keys, dict, sub_dicts}, parent_key) do
if struct do
[{_, child_key}] = Ecto.Model.primary_key!(struct)
child_key || raise Ecto.MissingPrimaryKeyError, struct: struct
end
# Traverse sub_structs adding one by one to the tree.
# Note we need to traverse even if we don't have a child_key
# due to nested associations.
{sub_dicts, sub_structs} =
Enum.map_reduce sub_dicts, sub_structs, &merge(&2, &1, child_key)
# Now if we have a struct and its parent key, we store the current
# data unless we have already processed it.
cache = {parent_key, child_key}
if struct && parent_key && not HashSet.member?(keys, cache) do
keys = HashSet.put(keys, cache)
item = {child_key, struct}
# If we have a list, we are at the root,
# so we also store the sub structs
dict =
if is_list(dict) do
[{item, sub_structs}|dict]
else
HashDict.update(dict, parent_key, [item], &[item|&1])
end
end
{{keys, dict, sub_dicts}, sub_structs}
end
defp load_assocs({child_key, struct}, sub_dicts, refls) do
Enum.reduce :lists.zip(sub_dicts, refls), struct, fn
{{_keys, dict, sub_dicts}, {refl, refls}}, acc ->
loaded =
dict
|> HashDict.get(child_key, [])
|> Enum.reverse()
|> Enum.map(&load_assocs(&1, sub_dicts, refls))
if refl.cardinality == :one do
loaded = List.first(loaded)
end
Map.put(acc, refl.field, loaded)
end
end
defp create_refls(idx, fields, sources) do
Enum.map(fields, fn {field, {child_idx, child_fields}} ->
{_source, model} = elem(sources, idx)
{model.__schema__(:association, field),
create_refls(child_idx, child_fields, sources)}
end)
end
defp create_accs(fields) do
acc = Enum.map(fields, fn {_field, {_child_idx, child_fields}} ->
create_accs(child_fields)
end)
{HashSet.new, HashDict.new, acc}
end
end