Class: PG::BasicTypeMapBasedOnResult

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 .new .

This class works equal to 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.

TypeMapByOid#build_column_map(result) can be used to generate a result independent 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 using text format.

Very similar with binary format:

conn.exec( "CREATE TEMP TABLE copytable (t TEXT, i INT, blob bytea, created_at timestamp)" )
# Retrieve table OIDs per empty result set in binary format.
res = conn.exec_params( "SELECT * FROM copytable LIMIT 0", [], 1 )
# 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::BinaryEncoder::CopyRow.new type_map: tm

conn.copy_data( "COPY copytable FROM STDIN WITH (FORMAT binary)", row_encoder ) do |res|
  conn.put_copy_data ['a', 123, "\xff\x00".b, Time.now]
end

This inserts a single row into copytable with type casts from ruby to database types using binary copy and value format. Binary COPY is faster than text format but less portable and less readable and pg offers fewer en-/decoders of database types.