Method: PG::Connection#copy_data
- Defined in:
- lib/pg/connection.rb
#copy_data(sql, coder = nil) ⇒ Object
call-seq:
conn.copy_data( sql [, coder] ) {|sql_result| ... } -> PG::Result
Execute a copy process for transferring data to or from the server.
This issues the SQL COPY command via #exec. The response to this (if there is no error in the command) is a PG::Result object that is passed to the block, bearing a status code of PGRES_COPY_OUT or PGRES_COPY_IN (depending on the specified copy direction). The application should then use #put_copy_data or #get_copy_data to receive or transmit data rows and should return from the block when finished.
#copy_data returns another PG::Result object when the data transfer is complete. An exception is raised if some problem was encountered, so it isn’t required to make use of any of them. At this point further SQL commands can be issued via #exec. (It is not possible to execute other SQL commands using the same connection while the COPY operation is in progress.)
This method ensures, that the copy process is properly terminated in case of client side or server side failures. Therefore, in case of blocking mode of operation, #copy_data is preferred to raw calls of #put_copy_data, #get_copy_data and #put_copy_end.
coder can be a PG::Coder derivation (typically PG::TextEncoder::CopyRow or PG::TextDecoder::CopyRow). This enables encoding of data fields given to #put_copy_data or decoding of fields received by #get_copy_data.
Example with CSV input format:
conn.exec "create table my_table (a text,b text,c text,d text)"
conn.copy_data "COPY my_table FROM STDIN CSV" do
conn.put_copy_data "some,data,to,copy\n"
conn.put_copy_data "more,data,to,copy\n"
end
This creates my_table
and inserts two CSV rows.
The same with text format encoder PG::TextEncoder::CopyRow and Array input:
enco = PG::TextEncoder::CopyRow.new
conn.copy_data "COPY my_table FROM STDIN", enco do
conn.put_copy_data ['some', 'data', 'to', 'copy']
conn.put_copy_data ['more', 'data', 'to', 'copy']
end
Also PG::BinaryEncoder::CopyRow can be used to send data in binary format to the server. In this case copy_data generates the header and trailer data automatically:
enco = PG::BinaryEncoder::CopyRow.new
conn.copy_data "COPY my_table FROM STDIN (FORMAT binary)", enco do
conn.put_copy_data ['some', 'data', 'to', 'copy']
conn.put_copy_data ['more', 'data', 'to', 'copy']
end
Example with CSV output format:
conn.copy_data "COPY my_table TO STDOUT CSV" do
while row=conn.get_copy_data
p row
end
end
This prints all rows of my_table
to stdout:
"some,data,to,copy\n"
"more,data,to,copy\n"
The same with text format decoder PG::TextDecoder::CopyRow and Array output:
deco = PG::TextDecoder::CopyRow.new
conn.copy_data "COPY my_table TO STDOUT", deco do
while row=conn.get_copy_data
p row
end
end
This receives all rows of my_table
as ruby array:
["some", "data", "to", "copy"]
["more", "data", "to", "copy"]
Also PG::BinaryDecoder::CopyRow can be used to retrieve data in binary format from the server. In this case the header and trailer data is processed by the decoder and the remaining nil
from get_copy_data is processed by copy_data, so that binary data can be processed equally to text data:
deco = PG::BinaryDecoder::CopyRow.new
conn.copy_data "COPY my_table TO STDOUT (FORMAT binary)", deco do
while row=conn.get_copy_data
p row
end
end
This receives all rows of my_table
as ruby array:
["some", "data", "to", "copy"]
["more", "data", "to", "copy"]
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# File 'lib/pg/connection.rb', line 211 def copy_data( sql, coder=nil ) raise PG::NotInBlockingMode.new("copy_data can not be used in nonblocking mode", connection: self) if nonblocking? res = exec( sql ) case res.result_status when PGRES_COPY_IN begin if coder && res.binary_tuples == 1 # Binary file header (11 byte signature, 32 bit flags and 32 bit extension length) put_copy_data(BinarySignature + ("\x00" * 8)) end if coder old_coder = self.encoder_for_put_copy_data self.encoder_for_put_copy_data = coder end yield res rescue Exception => err errmsg = "%s while copy data: %s" % [ err.class.name, err. ] begin put_copy_end( errmsg ) rescue PG::Error # Ignore error in cleanup to avoid losing original exception end discard_results raise err else begin self.encoder_for_put_copy_data = old_coder if coder if coder && res.binary_tuples == 1 put_copy_data("\xFF\xFF") # Binary file trailer 16 bit "-1" end put_copy_end rescue PG::Error => err raise PG::LostCopyState.new("#{err} (probably by executing another SQL query while running a COPY command)", connection: self) end get_last_result ensure self.encoder_for_put_copy_data = old_coder if coder end when PGRES_COPY_OUT begin if coder old_coder = self.decoder_for_get_copy_data self.decoder_for_get_copy_data = coder end yield res rescue Exception cancel discard_results raise else if coder && res.binary_tuples == 1 # There are two end markers in binary mode: file trailer and the final nil. # The file trailer is expected to be processed by BinaryDecoder::CopyRow and already returns nil, so that the remaining NULL from PQgetCopyData is retrieved here: if get_copy_data discard_results raise PG::NotAllCopyDataRetrieved.new("Not all binary COPY data retrieved", connection: self) end end res = get_last_result if !res discard_results raise PG::LostCopyState.new("Lost COPY state (probably by executing another SQL query while running a COPY command)", connection: self) elsif res.result_status != PGRES_COMMAND_OK discard_results raise PG::NotAllCopyDataRetrieved.new("Not all COPY data retrieved", connection: self) end res ensure self.decoder_for_get_copy_data = old_coder if coder end else raise ArgumentError, "SQL command is no COPY statement: #{sql}" end end |