BasicTypeMapBasedOnResult class

Simple set of rules for type casting common PostgreSQL types from Ruby to PostgreSQL.

OIDs of supported type casts are not hard-coded in the sources, but are retrieved from the PostgreSQL’s pg_type table in PG::BasicTypeMapBasedOnResult.new .

This class works equal to PG::BasicTypeMapForResults, but does not define decoders for the given result OIDs, but encoders. So it can be used to type cast field values based on the type OID retrieved by a separate SQL query.

PG::TypeMapByOid#build_column_map(result) can be used to generate a result independent PG::TypeMapByColumn type map, which can subsequently be used to cast query bind parameters or put_copy_data fields.

Example:

conn.exec( "CREATE TEMP TABLE copytable (t TEXT, i INT, ai INT[])" )

# Retrieve table OIDs per empty result set.
res = conn.exec( "SELECT * FROM copytable LIMIT 0" )
# Build a type map for common ruby to database type encoders.
btm = PG::BasicTypeMapBasedOnResult.new(conn)
# Build a PG::TypeMapByColumn with encoders suitable for copytable.
tm = btm.build_column_map( res )
row_encoder = PG::TextEncoder::CopyRow.new type_map: tm

conn.copy_data( "COPY copytable FROM STDIN", row_encoder ) do |res|
  conn.put_copy_data ['a', 123, [5,4,3]]
end

This inserts a single row into copytable with type casts from ruby to database types.

# File lib/pg/basic_type_map_based_on_result.rb, line 38
def initialize(connection_or_coder_maps, registry: nil)
        @coder_maps = build_coder_maps(connection_or_coder_maps, registry: registry)

        # Populate TypeMapByOid hash with encoders
        @coder_maps.each_format(:encoder).flat_map{|f| f.coders }.each do |coder|
                add_coder(coder)
        end
end