Class SQLite3::Database
In: lib/sqlite3/database.rb
Parent: Object

The Database class encapsulates a single connection to a SQLite3 database. Its usage is very straightforward:

  require 'sqlite3'

  db = SQLite3::Database.new( "data.db" )

  db.execute( "select * from table" ) do |row|
    p row
  end

  db.close

It wraps the lower-level methods provides by the selected driver, and includes the Pragmas module for access to various pragma convenience methods.

The Database class provides type translation services as well, by which the SQLite3 data types (which are all represented as strings) may be converted into their corresponding types (as defined in the schemas for their tables). This translation only occurs when querying data from the database—insertions and updates are all still typeless.

Furthermore, the Database class has been designed to work well with the ArrayFields module from Ara Howard. If you require the ArrayFields module before performing a query, and if you have not enabled results as hashes, then the results will all be indexible by field name.

Methods

Included Modules

Pragmas

Classes and Modules

Class SQLite3::Database::FunctionProxy

External Aliases

new -> open

Attributes

driver  [R]  A reference to the underlying SQLite3 driver used by this database.
handle  [R]  The low-level opaque database handle that this object wraps.
results_as_hash  [RW]  A boolean that indicates whether rows in result sets should be returned as hashes or not. By default, rows are returned as arrays.
type_translation  [RW]  A boolean indicating whether or not type translation is enabled for this database.

Public Class methods

Create a new Database object that opens the given file. If utf16 is true, the filename is interpreted as a UTF-16 encoded string.

By default, the new database will return result rows as arrays (results_as_hash) and has type translation disabled (type_translation=).

[Source]

     # File lib/sqlite3/database.rb, line 105
105:     def initialize( file_name, options={} )
106:       utf16 = options.fetch(:utf16, false)
107:       load_driver( options[:driver] )
108: 
109:       @statement_factory = options[:statement_factory] || Statement
110: 
111:       result, @handle = @driver.open( file_name, utf16 )
112:       Error.check( result, self, "could not open database" )
113: 
114:       @closed = false
115:       @results_as_hash = options.fetch(:results_as_hash,false)
116:       @type_translation = options.fetch(:type_translation,false)
117:       @translator = nil
118:       @transaction_active = false
119:     end

Quotes the given string, making it safe to use in an SQL statement. It replaces all instances of the single-quote character with two single-quote characters. The modified string is returned.

[Source]

    # File lib/sqlite3/database.rb, line 80
80:       def quote( string )
81:         string.gsub( /'/, "''" )
82:       end

Public Instance methods

Installs (or removes) a block that will be invoked for every access to the database. If the block returns 0 (or nil), the statement is allowed to proceed. Returning 1 causes an authorization error to occur, and returning 2 causes the access to be silently denied.

[Source]

     # File lib/sqlite3/database.rb, line 176
176:     def authorizer( data=nil, &block )
177:       result = @driver.set_authorizer( @handle, data, &block )
178:       Error.check( result, self )
179:     end

Register a busy handler with this database instance. When a requested resource is busy, this handler will be invoked. If the handler returns false, the operation will be aborted; otherwise, the resource will be requested again.

The handler will be invoked with the name of the resource that was busy, and the number of times it has been retried.

See also busy_timeout.

[Source]

     # File lib/sqlite3/database.rb, line 339
339:     def busy_handler( data=nil, &block ) # :yields: data, retries
340:       result = @driver.busy_handler( @handle, data, &block )
341:       Error.check( result, self )
342:     end

Indicates that if a request for a resource terminates because that resource is busy, SQLite should wait for the indicated number of milliseconds before trying again. By default, SQLite does not retry busy resources. To restore the default behavior, send 0 as the ms parameter.

See also busy_handler.

[Source]

     # File lib/sqlite3/database.rb, line 351
351:     def busy_timeout( ms )
352:       result = @driver.busy_timeout( @handle, ms )
353:       Error.check( result, self )
354:     end

Returns the number of changes made to this database instance by the last operation performed. Note that a "delete from table" without a where clause will not affect this value.

[Source]

     # File lib/sqlite3/database.rb, line 315
315:     def changes
316:       @driver.changes( @handle )
317:     end

Closes this database.

[Source]

     # File lib/sqlite3/database.rb, line 151
151:     def close
152:       unless @closed
153:         result = @driver.close( @handle )
154:         Error.check( result, self )
155:       end
156:       @closed = true
157:     end

Returns true if this database instance has been closed (see close).

[Source]

     # File lib/sqlite3/database.rb, line 160
160:     def closed?
161:       @closed
162:     end

Commits the current transaction. If there is no current transaction, this will cause an error to be raised. This returns true, in order to allow it to be used in idioms like abort? and rollback or commit.

[Source]

     # File lib/sqlite3/database.rb, line 610
610:     def commit
611:       execute "commit transaction"
612:       @transaction_active = false
613:       true
614:     end

Return true if the string is a valid (ie, parsable) SQL statement, and false otherwise. If +utf16+ is true, then the string is a UTF-16 character string.

[Source]

     # File lib/sqlite3/database.rb, line 124
124:     def complete?( string, utf16=false )
125:       @driver.complete?( string, utf16 )
126:     end

Creates a new aggregate function for use in SQL statements. Aggregate functions are functions that apply over every row in the result set, instead of over just a single row. (A very common aggregate function is the "count" function, for determining the number of rows that match a query.)

The new function will be added as name, with the given arity. (For variable arity functions, use -1 for the arity.)

The step parameter must be a proc object that accepts as its first parameter a FunctionProxy instance (representing the function invocation), with any subsequent parameters (up to the function’s arity). The step callback will be invoked once for each row of the result set.

The finalize parameter must be a proc object that accepts only a single parameter, the FunctionProxy instance representing the current function invocation. It should invoke FunctionProxy#set_result to store the result of the function.

Example:

  db.create_aggregate( "lengths", 1 ) do
    step do |func, value|
      func[ :total ] ||= 0
      func[ :total ] += ( value ? value.length : 0 )
    end

    finalize do |func|
      func.set_result( func[ :total ] || 0 )
    end
  end

  puts db.get_first_value( "select lengths(name) from table" )

See also create_aggregate_handler for a more object-oriented approach to aggregate functions.

[Source]

     # File lib/sqlite3/database.rb, line 435
435:     def create_aggregate( name, arity, step=nil, finalize=nil,
436:       text_rep=Constants::TextRep::ANY, &block )
437:     # begin
438:       if block
439:         proxy = AggregateDefinitionProxy.new
440:         proxy.instance_eval(&block)
441:         step ||= proxy.step_callback
442:         finalize ||= proxy.finalize_callback
443:       end
444: 
445:       step_callback = proc do |func,*args|
446:         ctx = @driver.aggregate_context( func )
447:         unless ctx[:__error]
448:           begin
449:             step.call( FunctionProxy.new( @driver, func, ctx ),
450:               *args.map{|v| Value.new(self,v)} )
451:           rescue Exception => e
452:             ctx[:__error] = e
453:           end
454:         end
455:       end
456: 
457:       finalize_callback = proc do |func|
458:         ctx = @driver.aggregate_context( func )
459:         unless ctx[:__error]
460:           begin
461:             finalize.call( FunctionProxy.new( @driver, func, ctx ) )
462:           rescue Exception => e
463:             @driver.result_error( func,
464:               "#{e.message} (#{e.class})", -1 )
465:           end
466:         else
467:           e = ctx[:__error]
468:           @driver.result_error( func,
469:             "#{e.message} (#{e.class})", -1 )
470:         end
471:       end
472: 
473:       result = @driver.create_function( @handle, name, arity, text_rep, nil,
474:         nil, step_callback, finalize_callback )
475:       Error.check( result, self )
476: 
477:       self
478:     end

This is another approach to creating an aggregate function (see create_aggregate). Instead of explicitly specifying the name, callbacks, arity, and type, you specify a factory object (the "handler") that knows how to obtain all of that information. The handler should respond to the following messages:

arity:corresponds to the arity parameter of create_aggregate. This message is optional, and if the handler does not respond to it, the function will have an arity of -1.
name:this is the name of the function. The handler must implement this message.
new:this must be implemented by the handler. It should return a new instance of the object that will handle a specific invocation of the function.

The handler instance (the object returned by the new message, described above), must respond to the following messages:

step:this is the method that will be called for each step of the aggregate function’s evaluation. It should implement the same signature as the step callback for create_aggregate.
finalize:this is the method that will be called to finalize the aggregate function’s evaluation. It should implement the same signature as the finalize callback for create_aggregate.

Example:

  class LengthsAggregateHandler
    def self.arity; 1; end

    def initialize
      @total = 0
    end

    def step( ctx, name )
      @total += ( name ? name.length : 0 )
    end

    def finalize( ctx )
      ctx.set_result( @total )
    end
  end

  db.create_aggregate_handler( LengthsAggregateHandler )
  puts db.get_first_value( "select lengths(name) from A" )

[Source]

     # File lib/sqlite3/database.rb, line 526
526:     def create_aggregate_handler( handler )
527:       arity = -1
528:       text_rep = Constants::TextRep::ANY
529: 
530:       arity = handler.arity if handler.respond_to?(:arity)
531:       text_rep = handler.text_rep if handler.respond_to?(:text_rep)
532:       name = handler.name
533: 
534:       step = proc do |func,*args|
535:         ctx = @driver.aggregate_context( func )
536:         unless ctx[ :__error ]
537:           ctx[ :handler ] ||= handler.new
538:           begin
539:             ctx[ :handler ].step( FunctionProxy.new( @driver, func, ctx ),
540:               *args.map{|v| Value.new(self,v)} )
541:           rescue Exception, StandardError => e
542:             ctx[ :__error ] = e
543:           end
544:         end
545:       end
546: 
547:       finalize = proc do |func|
548:         ctx = @driver.aggregate_context( func )
549:         unless ctx[ :__error ]
550:           ctx[ :handler ] ||= handler.new
551:           begin
552:             ctx[ :handler ].finalize( FunctionProxy.new( @driver, func, ctx ) )
553:           rescue Exception => e
554:             ctx[ :__error ] = e
555:           end
556:         end
557: 
558:         if ctx[ :__error ]
559:           e = ctx[ :__error ]
560:           @driver.sqlite3_result_error( func, "#{e.message} (#{e.class})", -1 )
561:         end
562:       end
563: 
564:       result = @driver.create_function( @handle, name, arity, text_rep, nil,
565:         nil, step, finalize )
566:       Error.check( result, self )
567: 
568:       self
569:     end

Creates a new function for use in SQL statements. It will be added as name, with the given arity. (For variable arity functions, use -1 for the arity.)

The block should accept at least one parameter—the FunctionProxy instance that wraps this function invocation—and any other arguments it needs (up to its arity).

The block does not return a value directly. Instead, it will invoke the FunctionProxy#set_result method on the func parameter and indicate the return value that way.

Example:

  db.create_function( "maim", 1 ) do |func, value|
    if value.nil?
      func.result = nil
    else
      func.result = value.split(//).sort.join
    end
  end

  puts db.get_first_value( "select maim(name) from table" )

[Source]

     # File lib/sqlite3/database.rb, line 379
379:     def create_function( name, arity, text_rep=Constants::TextRep::ANY,
380:       &block ) # :yields: func, *args
381:     # begin
382:       callback = proc do |func,*args|
383:         begin
384:           block.call( FunctionProxy.new( @driver, func ),
385:             *args.map{|v| Value.new(self,v)} )
386:         rescue StandardError, Exception => e
387:           @driver.result_error( func,
388:             "#{e.message} (#{e.class})", -1 )
389:         end
390:       end
391: 
392:       result = @driver.create_function( @handle, name, arity, text_rep, nil,
393:         callback, nil, nil )
394:       Error.check( result, self )
395: 
396:       self
397:     end

Return an integer representing the last error to have occurred with this database.

[Source]

     # File lib/sqlite3/database.rb, line 136
136:     def errcode
137:       @driver.errcode( @handle )
138:     end

Return a string describing the last error to have occurred with this database.

[Source]

     # File lib/sqlite3/database.rb, line 130
130:     def errmsg( utf16=false )
131:       @driver.errmsg( @handle, utf16 )
132:     end

Executes the given SQL statement. If additional parameters are given, they are treated as bind variables, and are bound to the placeholders in the query.

Note that if any of the values passed to this are hashes, then the key/value pairs are each bound separately, with the key being used as the name of the placeholder to bind the value to.

The block is optional. If given, it will be invoked for each row returned by the query. Otherwise, any results are accumulated into an array and returned wholesale.

See also execute2, query, and execute_batch for additional ways of executing statements.

[Source]

     # File lib/sqlite3/database.rb, line 210
210:     def execute( sql, *bind_vars )
211:       prepare( sql ) do |stmt|
212:         result = stmt.execute( *bind_vars )
213:         if block_given?
214:           result.each { |row| yield row }
215:         else
216:           return result.inject( [] ) { |arr,row| arr << row; arr }
217:         end
218:       end
219:     end

Executes the given SQL statement, exactly as with execute. However, the first row returned (either via the block, or in the returned array) is always the names of the columns. Subsequent rows correspond to the data from the result set.

Thus, even if the query itself returns no rows, this method will always return at least one row—the names of the columns.

See also execute, query, and execute_batch for additional ways of executing statements.

[Source]

     # File lib/sqlite3/database.rb, line 231
231:     def execute2( sql, *bind_vars )
232:       prepare( sql ) do |stmt|
233:         result = stmt.execute( *bind_vars )
234:         if block_given?
235:           yield result.columns
236:           result.each { |row| yield row }
237:         else
238:           return result.inject( [ result.columns ] ) { |arr,row|
239:             arr << row; arr }
240:         end
241:       end
242:     end

Executes all SQL statements in the given string. By contrast, the other means of executing queries will only execute the first statement in the string, ignoring all subsequent statements. This will execute each one in turn. The same bind parameters, if given, will be applied to each statement.

This always returns nil, making it unsuitable for queries that return rows.

[Source]

     # File lib/sqlite3/database.rb, line 252
252:     def execute_batch( sql, *bind_vars )
253:       sql = sql.strip
254:       until sql.empty? do
255:         prepare( sql ) do |stmt|
256:           stmt.execute( *bind_vars )
257:           sql = stmt.remainder.strip
258:         end
259:       end
260:       nil
261:     end

A convenience method for obtaining the first row of a result set, and discarding all others. It is otherwise identical to execute.

See also get_first_value.

[Source]

     # File lib/sqlite3/database.rb, line 291
291:     def get_first_row( sql, *bind_vars )
292:       execute( sql, *bind_vars ) { |row| return row }
293:       nil
294:     end

A convenience method for obtaining the first value of the first row of a result set, and discarding all other values and rows. It is otherwise identical to execute.

See also get_first_row.

[Source]

     # File lib/sqlite3/database.rb, line 301
301:     def get_first_value( sql, *bind_vars )
302:       execute( sql, *bind_vars ) { |row| return row[0] }
303:       nil
304:     end

Interrupts the currently executing operation, causing it to abort.

[Source]

     # File lib/sqlite3/database.rb, line 326
326:     def interrupt
327:       @driver.interrupt( @handle )
328:     end

Obtains the unique row ID of the last row to be inserted by this Database instance.

[Source]

     # File lib/sqlite3/database.rb, line 308
308:     def last_insert_row_id
309:       @driver.last_insert_rowid( @handle )
310:     end

Returns a Statement object representing the given SQL. This does not execute the statement; it merely prepares the statement for execution.

[Source]

     # File lib/sqlite3/database.rb, line 183
183:     def prepare( sql )
184:       stmt = @statement_factory.new( self, sql )
185:       if block_given?
186:         begin
187:           yield stmt
188:         ensure
189:           stmt.close
190:         end
191:       else
192:         return stmt
193:       end
194:     end

This is a convenience method for creating a statement, binding paramters to it, and calling execute:

  result = db.query( "select * from foo where a=?", 5 )
  # is the same as
  result = db.prepare( "select * from foo where a=?" ).execute( 5 )

You must be sure to call close on the ResultSet instance that is returned, or you could have problems with locks on the table. If called with a block, close will be invoked implicitly when the block terminates.

[Source]

     # File lib/sqlite3/database.rb, line 274
274:     def query( sql, *bind_vars )
275:       result = prepare( sql ).execute( *bind_vars )
276:       if block_given?
277:         begin
278:           yield result
279:         ensure
280:           result.close
281:         end
282:       else
283:         return result
284:       end
285:     end

Rolls the current transaction back. If there is no current transaction, this will cause an error to be raised. This returns true, in order to allow it to be used in idioms like abort? and rollback or commit.

[Source]

     # File lib/sqlite3/database.rb, line 620
620:     def rollback
621:       execute "rollback transaction"
622:       @transaction_active = false
623:       true
624:     end

Returns the total number of changes made to this database instance since it was opened.

[Source]

     # File lib/sqlite3/database.rb, line 321
321:     def total_changes
322:       @driver.total_changes( @handle )
323:     end

Installs (or removes) a block that will be invoked for every SQL statement executed. The block receives a two parameters: the data argument, and the SQL statement executed. If the block is nil, any existing tracer will be uninstalled.

[Source]

     # File lib/sqlite3/database.rb, line 168
168:     def trace( data=nil, &block )
169:       @driver.trace( @handle, data, &block )
170:     end

Begins a new transaction. Note that nested transactions are not allowed by SQLite, so attempting to nest a transaction will result in a runtime exception.

The mode parameter may be either :deferred (the default), :immediate, or :exclusive.

If a block is given, the database instance is yielded to it, and the transaction is committed when the block terminates. If the block raises an exception, a rollback will be performed instead. Note that if a block is given, commit and rollback should never be called explicitly or you’ll get an error when the block terminates.

If a block is not given, it is the caller’s responsibility to end the transaction explicitly, either by calling commit, or by calling rollback.

[Source]

     # File lib/sqlite3/database.rb, line 587
587:     def transaction( mode = :deferred )
588:       execute "begin #{mode.to_s} transaction"
589:       @transaction_active = true
590: 
591:       if block_given?
592:         abort = false
593:         begin
594:           yield self
595:         rescue ::Object
596:           abort = true
597:           raise
598:         ensure
599:           abort and rollback or commit
600:         end
601:       end
602: 
603:       true
604:     end

Returns true if there is a transaction active, and false otherwise.

[Source]

     # File lib/sqlite3/database.rb, line 627
627:     def transaction_active?
628:       @transaction_active
629:     end

Return the type translator employed by this database instance. Each database instance has its own type translator; this allows for different type handlers to be installed in each instance without affecting other instances. Furthermore, the translators are instantiated lazily, so that if a database does not use type translation, it will not be burdened by the overhead of a useless type translator. (See the Translator class.)

[Source]

     # File lib/sqlite3/database.rb, line 146
146:     def translator
147:       @translator ||= Translator.new
148:     end

[Validate]