This is the interface to allow Blob objects to be written to and read from the SQLite database. When using statements, use a Blob object as the wrapper around the source to be written to the row, and a Blob object is returned if the the type mapping warrents during select queries.
For instance during an insert:
blob_column = db.schema.tables['blobs'].columns['data'] db.execute("INSERT INTO blobs(name, data) VALUES ( $name, $blob )", { "$name" => "/path/to/file", "$blob" => Amalgalite::Blob.new( :file => '/path/to/file', :column => blob_column) } ) db.execute("INSERT INTO blobs(id, data) VALUES ($id, $blob )", { "$name" => 'blobname', "$blob" => Amalgalite::Blob.new( :io => "something with .read and .length methods", :column => blob_column) } )
On select the blob data needs to be read into an IO object
all_rows = db.execute("SELECT name, blob FROM blobs WHERE name = '/path/to/file' ") blob_row = all_rows.first blob_row['blob'].write_to_file( blob_row['name'] )
Or write to an IO object
blob_results = {} db.execute("SELECT name, blob FROM blobs") do |row| io = StringIO.new row['blob'].write_to_io( io ) blob_results[row['name']] = io # or use a shortcut # blob_results[row['name']] = row['blob'].to_string_io end
If using a Blob as a conditional, for instance in a WHERE clause then the Blob must resolvable to a String.
db.execute("SELECT FROM blobs(name, data) WHERE data = $blob", { "$blob' => Amalgalite::Blob.new( :string => "A string of data" ) })
# File lib/amalgalite/blob.rb, line 55 def default_block_size @default_block_size ||= 8192 end
Initialize a new blob, it takes a single parameter, a hash which describes the source of the blob. The keys of the hash are one of:
:file : the value is the path to a file on the file system :io : the value is an object that responds to the the methods +read+ and +length+. +read+ should have the behavior of IO#read :db_blob : not normally used by an end user, used to initialize a blob object that is returned from an SQL query. :string : used when a Blob is part of a WHERE clause or result
And additional key of :block_size may be used to indicate the maximum size of a single block of data to move from the source to the destination, this defaults ot 8192.
# File lib/amalgalite/blob.rb, line 87 def initialize( params ) if (Blob.valid_source_params & params.keys).size > 1 then raise Blob::Error, "Only a one of #{Blob.valid_source_params.join(', ')} is allowed to initialize a Blob. #{params.keys.join(', ')} were sent" end @source = nil @source_length = 0 @close_source_after_read = false @incremental = true @block_size = params[:block_size] || Blob.default_block_size @column = params[:column] raise Blob::Error, "A :column parameter is required for a Blob" unless @column or params.has_key?( :string ) if params.has_key?( :file ) then @source = File.open( params[:file], "r" ) @length = File.size( params[:file] ) @close_source_after_read = true elsif params.has_key?( :io ) then @source = params[:io] @length = @source.length elsif params.has_key?( :db_blob ) then @source = params[:db_blob] @length = @source.length @close_source_after_read = true elsif params.has_key?( :string ) then @source = params[:string] @length = @source.length @incremental = false end end
close the source when done reading from it
# File lib/amalgalite/blob.rb, line 122 def close_source_after_read? @close_source_after_read end
is this an incremental Blob or not
# File lib/amalgalite/blob.rb, line 129 def incremental? @incremental end
conver the blob to a string
# File lib/amalgalite/blob.rb, line 153 def to_s to_string_io.string end
write the Blob contents to a StringIO
# File lib/amalgalite/blob.rb, line 160 def to_string_io sio = StringIO.new write_to_io( sio ) return sio end
Write the Blob contents to the column. This assumes that the row_id to insert into is the last row that was inserted into the db
# File lib/amalgalite/blob.rb, line 179 def write_to_column! last_rowid = column.schema.db.last_insert_rowid SQLite3::Blob.new( column.schema.db.api, column.db, column.table, column.name, last_rowid, "w" ) do |sqlite_blob| write_to_io( sqlite_blob ) end end
Write the Blob contents to a File.
# File lib/amalgalite/blob.rb, line 169 def write_to_file( filename, modestring="w" ) File.open(filename, modestring) do |f| write_to_io( f ) end end
Write the Blob to an IO object
# File lib/amalgalite/blob.rb, line 136 def write_to_io( io ) if source.respond_to?( :read ) then while buf = source.read( block_size ) do io.write( buf ) end else io.write( source.to_s ) end if close_source_after_read? then source.close end end
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