# 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 `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.

### Public Class Methods

new(connection) click to toggle source

    # File lib/pg/basic_type_mapping.rb, line 369
    def initialize(connection)
            @coder_maps = build_coder_maps(connection)

            # Populate TypeMapByOid hash with encoders
            @coder_maps.map{|f| f[:encoder].coders }.flatten.each do |coder|
                    add_coder(coder)
            end
    end