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Only traverse the solution set to remove blank nodes when necessary

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Also add an option remove_bnode_query_variables to skip the removal
generally.
This commit is contained in:
Marcel Otto 2020-06-05 12:33:04 +02:00
parent ef218a3a90
commit f4bda2ef00
2 changed files with 34 additions and 13 deletions
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2
lib/rdf/query/bgp.ex
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@ -6,6 +6,6 @@ defmodule RDF.Query.BGP do
@type solution :: map
@type solutions :: [solution]
@callback query(triple_patterns :: [], data :: RDF.Data.t) :: solutions
@callback query(triple_patterns :: [], data :: RDF.Data.t, opts :: Keyword.t) :: solutions
end

45
lib/rdf/query/bgp/simple.ex
View file

@ -52,24 +52,45 @@ defmodule RDF.Query.BGP.Simple do
@blank_node_prefix "_:"
@default_remove_bnode_query_variables Application.get_env(:rdf, :default_remove_bnode_query_variables, true)
@impl RDF.Query.BGP
def query(data, pattern)
def query(data, pattern, opts \\ [])
def query(_, []), do: [%{}] # https://www.w3.org/TR/sparql11-query/#emptyGroupPattern
def query(_, [], _), do: [%{}] # https://www.w3.org/TR/sparql11-query/#emptyGroupPattern
def query(data, triple_patterns) do
triple_patterns
|> Stream.map(&convert_blank_nodes/1)
|> Planner.query_plan()
|> do_query(data)
|> Enum.map(&remove_blank_nodes/1)
def query(data, triple_patterns, opts) do
{has_blank_nodes, triple_patterns} = preprocess(triple_patterns)
solutions =
triple_patterns
|> Planner.query_plan()
|> do_query(data)
if has_blank_nodes and
Keyword.get(opts, :remove_bnode_query_variables, @default_remove_bnode_query_variables) do
Enum.map(solutions, &remove_blank_nodes/1)
else
solutions
end
end
defp preprocess(triple_patterns) do
Enum.reduce(triple_patterns, {false, []}, fn
original_triple_pattern, {had_blank_nodes, triple_patterns} ->
{is_converted, triple_pattern} = convert_blank_nodes(original_triple_pattern)
{had_blank_nodes || is_converted, [triple_pattern | triple_patterns]}
end)
end
defp convert_blank_nodes({%BlankNode{} = s, p, o}), do: convert_blank_nodes({to_string(s), p, o})
defp convert_blank_nodes({s, %BlankNode{} = p, o}), do: convert_blank_nodes({s, to_string(p), o})
defp convert_blank_nodes({s, p, %BlankNode{} = o}), do: convert_blank_nodes({s, p, to_string(o)})
defp convert_blank_nodes(triple_pattern), do: triple_pattern
defp convert_blank_nodes({%BlankNode{} = s, %BlankNode{} = p, %BlankNode{} = o}), do: {true, {to_string(s), to_string(p), to_string(o)}}
defp convert_blank_nodes({s, %BlankNode{} = p, %BlankNode{} = o}), do: {true, {s, to_string(p), to_string(o)}}
defp convert_blank_nodes({%BlankNode{} = s, p, %BlankNode{} = o}), do: {true, {to_string(s), p, to_string(o)}}
defp convert_blank_nodes({%BlankNode{} = s, %BlankNode{} = p, o}), do: {true, {to_string(s), to_string(p), o}}
defp convert_blank_nodes({%BlankNode{} = s, p, o}), do: {true, {to_string(s), p, o}}
defp convert_blank_nodes({s, %BlankNode{} = p, o}), do: {true, {s, to_string(p), o}}
defp convert_blank_nodes({s, p, %BlankNode{} = o}), do: {true, {s, p, to_string(o)}}
defp convert_blank_nodes(triple_pattern), do: {false, triple_pattern}
defp remove_blank_nodes(solution) do
solution