Class: SQLite3::Database

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

- authorizer
- busy_handler
- busy_timeout
- changes
- close
- closed?
- commit
- complete?
- create_aggregate
- create_aggregate_handler
- create_function
- errcode
- errmsg
- execute
- execute2
- execute_batch
- get_first_row
- get_first_value
- interrupt
- last_insert_row_id
- new
- prepare
- query
- quote
- rollback
- total_changes
- trace
- transaction
- transaction_active?
- translator

Included Modules

- Pragmas

Attributes

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

Classes and Modules
Class SQLite3::Database::FunctionProxy
Public Class methods
new( file_name, options={} )

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=).

[ show 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, nil, "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:     end

quote( string )

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.

[ show source ]

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

Public Instance methods
authorizer( data=nil, &block )

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 175
    175:     def authorizer( data=nil, &block )
    176:       result = @driver.set_authorizer( @handle, data, &block )
    177:       Error.check( result, self )
    178:     end

busy_handler( data=nil ) {|data, retries| ...}

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 338
    338:     def busy_handler( data=nil, &block ) # :yields: data, retries
    339:       result = @driver.busy_handler( @handle, data, &block )
    340:       Error.check( result, self )
    341:     end

busy_timeout( ms )

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 350
    350:     def busy_timeout( ms )
    351:       result = @driver.busy_timeout( @handle, ms )
    352:       Error.check( result, self )
    353:     end

changes()

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 314
    314:     def changes
    315:       @driver.changes( @handle )
    316:     end

close()

Closes this database.

[ show source ]

         # File lib/sqlite3/database.rb, line 150
    150:     def close
    151:       unless @closed
    152:         result = @driver.close( @handle )
    153:         Error.check( result, self )
    154:       end
    155:       @closed = true
    156:     end

closed?()

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

[ show source ]

         # File lib/sqlite3/database.rb, line 159
    159:     def closed?
    160:       @closed
    161:     end

commit()

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`.

[ show source ]

         # File lib/sqlite3/database.rb, line 609
    609:     def commit
    610:       execute "commit transaction"
    611:       @transaction_active = false
    612:       true
    613:     end

complete?( string, utf16=false )

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 123
    123:     def complete?( string, utf16=false )
    124:       @driver.complete?( string, utf16 )
    125:     end

create_aggregate( name, arity, step=nil, finalize=nil, text_rep=Constants::TextRep::ANY, &block )

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 434
    434:     def create_aggregate( name, arity, step=nil, finalize=nil,
    435:       text_rep=Constants::TextRep::ANY, &block )
    436:     # begin
    437:       if block
    438:         proxy = AggregateDefinitionProxy.new
    439:         proxy.instance_eval &block
    440:         step ||= proxy.step_callback
    441:         finalize ||= proxy.finalize_callback
    442:       end
    443:
    444:       step_callback = proc do |func,*args|
    445:         ctx = @driver.aggregate_context( func )
    446:         unless ctx[:__error]
    447:           begin
    448:             step.call( FunctionProxy.new( @driver, func, ctx ),
    449:               *args.map{|v| Value.new(self,v)} )
    450:           rescue Exception => e
    451:             ctx[:__error] = e
    452:           end
    453:         end
    454:       end
    455:
    456:       finalize_callback = proc do |func|
    457:         ctx = @driver.aggregate_context( func )
    458:         unless ctx[:__error]
    459:           begin
    460:             finalize.call( FunctionProxy.new( @driver, func, ctx ) )
    461:           rescue Exception => e
    462:             @driver.result_error( func,
    463:               "#{e.message} (#{e.class})", -1 )
    464:           end
    465:         else
    466:           e = ctx[:__error]
    467:           @driver.result_error( func,
    468:             "#{e.message} (#{e.class})", -1 )
    469:         end
    470:       end
    471:
    472:       result = @driver.create_function( @handle, name, arity, text_rep, nil,
    473:         nil, step_callback, finalize_callback )
    474:       Error.check( result, self )
    475:
    476:       self
    477:     end

create_aggregate_handler( handler )

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" )

[ show source ]

         # File lib/sqlite3/database.rb, line 525
    525:     def create_aggregate_handler( handler )
    526:       arity = -1
    527:       text_rep = Constants::TextRep::ANY
    528:
    529:       arity = handler.arity if handler.respond_to?(:arity)
    530:       text_rep = handler.text_rep if handler.respond_to?(:text_rep)
    531:       name = handler.name
    532:
    533:       step = proc do |func,*args|
    534:         ctx = @driver.aggregate_context( func )
    535:         unless ctx[ :__error ]
    536:           ctx[ :handler ] ||= handler.new
    537:           begin
    538:             ctx[ :handler ].step( FunctionProxy.new( @driver, func, ctx ),
    539:               *args.map{|v| Value.new(self,v)} )
    540:           rescue Exception, StandardError => e
    541:             ctx[ :__error ] = e
    542:           end
    543:         end
    544:       end
    545:
    546:       finalize = proc do |func|
    547:         ctx = @driver.aggregate_context( func )
    548:         unless ctx[ :__error ]
    549:           ctx[ :handler ] ||= handler.new
    550:           begin
    551:             ctx[ :handler ].finalize( FunctionProxy.new( @driver, func, ctx ) )
    552:           rescue Exception => e
    553:             ctx[ :__error ] = e
    554:           end
    555:         end
    556:
    557:         if ctx[ :__error ]
    558:           e = ctx[ :__error ]
    559:           @driver.sqlite3_result_error( func, "#{e.message} (#{e.class})", -1 )
    560:         end
    561:       end
    562:
    563:       result = @driver.create_function( @handle, name, arity, text_rep, nil,
    564:         nil, step, finalize )
    565:       Error.check( result, self )
    566:
    567:       self
    568:     end

create_function( name, arity, text_rep=Constants::TextRep::ANY ) {|func, *args| ...}

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" )

[ show source ]

         # File lib/sqlite3/database.rb, line 378
    378:     def create_function( name, arity, text_rep=Constants::TextRep::ANY,
    379:       &block ) # :yields: func, *args
    380:     # begin
    381:       callback = proc do |func,*args|
    382:         begin
    383:           block.call( FunctionProxy.new( @driver, func ),
    384:             *args.map{|v| Value.new(self,v)} )
    385:         rescue StandardError, Exception => e
    386:           @driver.result_error( func,
    387:             "#{e.message} (#{e.class})", -1 )
    388:         end
    389:       end
    390:
    391:       result = @driver.create_function( @handle, name, arity, text_rep, nil,
    392:         callback, nil, nil )
    393:       Error.check( result, self )
    394:
    395:       self
    396:     end

errcode()

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

[ show source ]

         # File lib/sqlite3/database.rb, line 135
    135:     def errcode
    136:       @driver.errcode( @handle )
    137:     end

errmsg( utf16=false )

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

[ show source ]

         # File lib/sqlite3/database.rb, line 129
    129:     def errmsg( utf16=false )
    130:       @driver.errmsg( @handle, utf16 )
    131:     end

execute( sql, *bind_vars ) {|row| ...}

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 209
    209:     def execute( sql, *bind_vars )
    210:       prepare( sql ) do |stmt|
    211:         result = stmt.execute( *bind_vars )
    212:         if block_given?
    213:           result.each { |row| yield row }
    214:         else
    215:           return result.inject( [] ) { |arr,row| arr << row; arr }
    216:         end
    217:       end
    218:     end

execute2( sql, *bind_vars ) {|result.columns| ...}

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 230
    230:     def execute2( sql, *bind_vars )
    231:       prepare( sql ) do |stmt|
    232:         result = stmt.execute( *bind_vars )
    233:         if block_given?
    234:           yield result.columns
    235:           result.each { |row| yield row }
    236:         else
    237:           return result.inject( [ result.columns ] ) { |arr,row|
    238:             arr << row; arr }
    239:         end
    240:       end
    241:     end

execute_batch( sql, *bind_vars )

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 251
    251:     def execute_batch( sql, *bind_vars )
    252:       sql = sql.strip
    253:       until sql.empty? do
    254:         prepare( sql ) do |stmt|
    255:           stmt.execute( *bind_vars )
    256:           sql = stmt.remainder.strip
    257:         end
    258:       end
    259:       nil
    260:     end

get_first_row( sql, *bind_vars )

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 290
    290:     def get_first_row( sql, *bind_vars )
    291:       execute( sql, *bind_vars ) { |row| return row }
    292:       nil
    293:     end

get_first_value( sql, *bind_vars )

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 300
    300:     def get_first_value( sql, *bind_vars )
    301:       execute( sql, *bind_vars ) { |row| return row[0] }
    302:       nil
    303:     end

interrupt()

Interrupts the currently executing operation, causing it to abort.

[ show source ]

         # File lib/sqlite3/database.rb, line 325
    325:     def interrupt
    326:       @driver.interrupt( @handle )
    327:     end

last_insert_row_id()

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

[ show source ]

         # File lib/sqlite3/database.rb, line 307
    307:     def last_insert_row_id
    308:       @driver.last_insert_rowid( @handle )
    309:     end

prepare( sql ) {|stmt| ...}

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

[ show source ]

         # File lib/sqlite3/database.rb, line 182
    182:     def prepare( sql )
    183:       stmt = @statement_factory.new( self, sql )
    184:       if block_given?
    185:         begin
    186:           yield stmt
    187:         ensure
    188:           stmt.close
    189:         end
    190:       else
    191:         return stmt
    192:       end
    193:     end

query( sql, *bind_vars ) {|result| ...}

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 273
    273:     def query( sql, *bind_vars )
    274:       result = prepare( sql ).execute( *bind_vars )
    275:       if block_given?
    276:         begin
    277:           yield result
    278:         ensure
    279:           result.close
    280:         end
    281:       else
    282:         return result
    283:       end
    284:     end

rollback()

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`.

[ show source ]

         # File lib/sqlite3/database.rb, line 619
    619:     def rollback
    620:       execute "rollback transaction"
    621:       @transaction_active = false
    622:       true
    623:     end

total_changes()

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

[ show source ]

         # File lib/sqlite3/database.rb, line 320
    320:     def total_changes
    321:       @driver.total_changes( @handle )
    322:     end

trace( data=nil, &block )

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 167
    167:     def trace( data=nil, &block )
    168:       @driver.trace( @handle, data, &block )
    169:     end

transaction( mode = :deferred ) {|self| ...}

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.

[ show source ]

         # File lib/sqlite3/database.rb, line 586
    586:     def transaction( mode = :deferred )
    587:       execute "begin #{mode.to_s} transaction"
    588:       @transaction_active = true
    589:
    590:       if block_given?
    591:         abort = false
    592:         begin
    593:           yield self
    594:         rescue Exception
    595:           abort = true
    596:           raise
    597:         ensure
    598:           abort and rollback or commit
    599:         end
    600:       end
    601:
    602:       true
    603:     end

transaction_active?()

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

[ show source ]

         # File lib/sqlite3/database.rb, line 626
    626:     def transaction_active?
    627:       @transaction_active
    628:     end

translator()

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.)

[ show source ]

         # File lib/sqlite3/database.rb, line 145
    145:     def translator
    146:       @translator ||= Translator.new
    147:     end

[Validate]