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

  require 'sqlite'

  db = SQLite::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 API module, include includes the Pragmas module for access to various pragma convenience methods.

The Database class provides type translation services as well, by which the SQLite 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
Attributes
[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.
Classes and Modules
Class SQLite::Database::FunctionProxy
Public Class methods
complete?( string )

Return true if the string is a valid (ie, parsable) SQL statement, and false otherwise.

     # File lib/sqlite/database.rb, line 99
 99:     def self.complete?( string )
100:       SQLite::API.complete( string )
101:     end
decode( string )

Unserializes the object contained in the given string. The string must be one that was returned by encode.

    # File lib/sqlite/database.rb, line 93
93:     def self.decode( string )
94:       Marshal.load( Base64.decode64( string ) )
95:     end
encode( object )

Returns a string that represents the serialization of the given object. The string may safely be used in an SQL statement.

    # File lib/sqlite/database.rb, line 87
87:     def self.encode( object )
88:       Base64.encode64( Marshal.dump( object ) ).strip
89:     end
new( file_name, mode=0 )

Create a new Database object that opens the given file. The mode parameter has no meaning yet, and may be omitted. If the file does not exist, it will be created if possible.

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

     # File lib/sqlite/database.rb, line 116
116:     def initialize( file_name, mode=0 )
117:       @handle = SQLite::API.open( file_name, mode )
118:       @closed = false
119:       @results_as_hash = false
120:       @type_translation = false
121:       @translator = nil
122:     end
open( file_name )

Opens the database contained in the given file. This just calls new, passing 0 as the mode parameter. This returns the new Database instance.

    # File lib/sqlite/database.rb, line 74
74:     def self.open( file_name )
75:       new( file_name, 0 )
76:     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.

    # File lib/sqlite/database.rb, line 81
81:     def self.quote( string )
82:       string.gsub( /'/, "''" )
83:     end
Public Instance methods
busy_handler( ) {|resource, 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.

     # File lib/sqlite/database.rb, line 307
307:     def busy_handler( &block ) # :yields: resource, retries
308:       SQLite::API.busy_handler( @handle, block )
309:     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.

     # File lib/sqlite/database.rb, line 318
318:     def busy_timeout( ms )
319:       SQLite::API.busy_timeout( @handle, ms )
320:     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.

     # File lib/sqlite/database.rb, line 289
289:     def changes
290:       SQLite::API.changes( @handle )
291:     end
close()

Closes this database. No checks are done to ensure that a database is not closed more than once, and closing a database more than once can be catastrophic.

     # File lib/sqlite/database.rb, line 148
148:     def close
149:       SQLite::API.close( @handle )
150:       @closed = true
151:     end
closed?()

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

     # File lib/sqlite/database.rb, line 154
154:     def closed?
155:       @closed
156:     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.

     # File lib/sqlite/database.rb, line 593
593:     def commit
594:       execute "commit transaction"
595:       @transaction_active = false
596:       true
597:     end
create_aggregate( name, arity, step, finalize, type=nil )

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.) If type is non-nil, it should be a value as described in create_function.

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:

  step = proc do |func, value|
    func[ :total ] ||= 0
    func[ :total ] += ( value ? value.length : 0 )
  end

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

  db.create_aggregate( "lengths", 1, step, finalize, :numeric )

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

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

     # File lib/sqlite/database.rb, line 411
411:     def create_aggregate( name, arity, step, finalize, type=nil )
412:       case type
413:         when :numeric
414:           type = SQLite::API::NUMERIC
415:         when :text
416:           type = SQLite::API::TEXT
417:         when :args
418:           type = SQLite::API::ARGS
419:       end
420: 
421:       step_callback = proc do |func,*args|
422:         ctx = SQLite::API.aggregate_context( func )
423:         unless ctx[:__error]
424:           begin
425:             step.call( FunctionProxy.new( func, ctx ), *args )
426:           rescue Exception => e
427:             ctx[:__error] = e
428:           end
429:         end
430:       end
431: 
432:       finalize_callback = proc do |func|
433:         ctx = SQLite::API.aggregate_context( func )
434:         unless ctx[:__error]
435:           begin
436:             finalize.call( FunctionProxy.new( func, ctx ) )
437:           rescue Exception => e
438:             SQLite::API.set_result_error( func, "#{e.message} (#{e.class})" )
439:           end
440:         else
441:           e = ctx[:__error]
442:           SQLite::API.set_result_error( func, "#{e.message} (#{e.class})" )
443:         end
444:       end
445: 
446:       SQLite::API.create_aggregate( @handle, name, arity,
447:         step_callback, finalize_callback )
448: 
449:       SQLite::API.function_type( @handle, name, type ) if type
450: 
451:       self
452:     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:

function_type:corresponds to the type parameter of create_aggregate. This is an optional message, and if the handler does not respond to it, the function type will not be set for this function.
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.function_type; :numeric; end
    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" )
     # File lib/sqlite/database.rb, line 505
505:     def create_aggregate_handler( handler )
506:       type = nil
507:       arity = -1
508: 
509:       type = handler.function_type if handler.respond_to?(:function_type)
510:       arity = handler.arity if handler.respond_to?(:arity)
511:       name = handler.name
512: 
513:       case type
514:         when :numeric
515:           type = SQLite::API::NUMERIC
516:         when :text
517:           type = SQLite::API::TEXT
518:         when :args
519:           type = SQLite::API::ARGS
520:       end
521: 
522:       step = proc do |func,*args|
523:         ctx = SQLite::API.aggregate_context( func )
524:         unless ctx[ :__error ]
525:           ctx[ :handler ] ||= handler.new
526:           begin
527:             ctx[ :handler ].step( FunctionProxy.new( func, ctx ), *args )
528:           rescue Exception => e
529:             ctx[ :__error ] = e
530:           end
531:         end
532:       end
533: 
534:       finalize = proc do |func|
535:         ctx = SQLite::API.aggregate_context( func )
536:         unless ctx[ :__error ]
537:           ctx[ :handler ] ||= handler.new
538:           begin
539:             ctx[ :handler ].finalize( FunctionProxy.new( func, ctx ) )
540:           rescue Exception => e
541:             ctx[ :__error ] = e
542:           end
543:         end
544: 
545:         if ctx[ :__error ]
546:           e = ctx[ :__error ]
547:           SQLite::API.set_result_error( func, "#{e.message} (#{e.class})" )
548:         end
549:       end
550: 
551:       SQLite::API.create_aggregate( @handle, name, arity, step, finalize )
552:       SQLite::API.function_type( @handle, name, type ) if type
553: 
554:       self
555:     end
create_function( name, arity, type=nil ) {|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.) If type is non-nil, it should either be an integer (indicating that the type of the function is always the type of the argument at that index), or one of the symbols :numeric, :text, :args (in which case the function is, respectively, numeric, textual, or the same type as its arguments).

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, :text ) do |func, value|
    if value.nil?
      func.set_value nil
    else
      func.set_value value.split(//).sort.join
    end
  end

  puts db.get_first_value( "select maim(name) from table" )
     # File lib/sqlite/database.rb, line 350
350:     def create_function( name, arity, type=nil, &block ) # :yields: func, *args
351:       case type
352:         when :numeric
353:           type = SQLite::API::NUMERIC
354:         when :text
355:           type = SQLite::API::TEXT
356:         when :args
357:           type = SQLite::API::ARGS
358:       end
359: 
360:       callback = proc do |func,*args|
361:         begin
362:           block.call( FunctionProxy.new( func ), *args )
363:         rescue Exception => e
364:           SQLite::API.set_result_error( func, "#{e.message} (#{e.class})" )
365:         end
366:       end
367: 
368:       SQLite::API.create_function( @handle, name, arity, callback )
369:       SQLite::API.function_type( @handle, name, type ) if type
370: 
371:       self
372:     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.

Each placeholder must match one of the following formats:

  • ?
  • ?nnn
  • :word
  • :word:

where nnn is an integer value indicating the index of the bind variable to be bound at that position, and word is an alphanumeric identifier for that placeholder. For "?", an index is automatically assigned of one greater than the previous index used (or 1, if it is the first).

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, execute_batch and query for additional ways of executing statements.

     # File lib/sqlite/database.rb, line 191
191:     def execute( sql, *bind_vars )
192:       stmt = prepare( sql )
193:       stmt.bind_params( *bind_vars )
194:       result = stmt.execute
195:       begin
196:         if block_given?
197:           result.each { |row| yield row }
198:         else
199:           return result.inject( [] ) { |arr,row| arr << row; arr }
200:         end
201:       ensure
202:         result.close
203:       end
204:     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, execute_batch and query for additional ways of executing statements.

     # File lib/sqlite/database.rb, line 216
216:     def execute2( sql, *bind_vars )
217:       stmt = prepare( sql )
218:       stmt.bind_params( *bind_vars )
219:       result = stmt.execute
220:       begin
221:         if block_given?
222:           yield result.columns
223:           result.each { |row| yield row }
224:         else
225:           return result.inject( [ result.columns ] ) { |arr,row| arr << row; arr }
226:         end
227:       ensure  
228:         result.close
229:       end
230:     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.

     # File lib/sqlite/database.rb, line 240
240:     def execute_batch( sql, *bind_vars )
241:       loop do
242:         stmt = prepare( sql )
243:         stmt.bind_params *bind_vars
244:         stmt.execute
245:         sql = stmt.remainder
246:         break if sql.length < 1
247:       end
248:       nil
249:     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.

     # File lib/sqlite/database.rb, line 265
265:     def get_first_row( sql, *bind_vars )
266:       execute( sql, *bind_vars ) { |row| return row }
267:       nil
268:     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.

     # File lib/sqlite/database.rb, line 275
275:     def get_first_value( sql, *bind_vars )
276:       execute( sql, *bind_vars ) { |row| return row[0] }
277:       nil
278:     end
interrupt()

Interrupts the currently executing operation, causing it to abort.

     # File lib/sqlite/database.rb, line 294
294:     def interrupt
295:       SQLite::API.interrupt( @handle )
296:     end
last_insert_row_id()

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

     # File lib/sqlite/database.rb, line 282
282:     def last_insert_row_id
283:       SQLite::API.last_insert_row_id( @handle )
284:     end
prepare( sql )

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

     # File lib/sqlite/database.rb, line 160
160:     def prepare( sql )
161:       Statement.new( self, sql )
162:     end
query( sql, *bind_vars ) {|result_set| ...}

This does like execute and execute2 (binding variables and so forth), but instead of yielding each row from the result set, this will yield the ResultSet instance itself (q.v.). If no block is given, the ResultSet instance will be returned.

     # File lib/sqlite/database.rb, line 255
255:     def query( sql, *bind_vars, &block ) # :yields: result_set
256:       stmt = prepare( sql )
257:       stmt.bind_params( *bind_vars )
258:       stmt.execute( &block )
259:     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.

     # File lib/sqlite/database.rb, line 603
603:     def rollback
604:       execute "rollback transaction"
605:       @transaction_active = false
606:       true
607:     end
transaction() {|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.

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.

     # File lib/sqlite/database.rb, line 570
570:     def transaction
571:       execute "begin transaction"
572:       @transaction_active = true
573: 
574:       if block_given?
575:         abort = false
576:         begin
577:           yield self
578:         rescue Exception
579:           abort = true
580:           raise
581:         ensure
582:           abort and rollback or commit
583:         end
584:       end
585: 
586:       true
587:     end
transaction_active?()

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

     # File lib/sqlite/database.rb, line 610
610:     def transaction_active?
611:       @transaction_active
612:     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.)

     # File lib/sqlite/database.rb, line 130
130:     def translator
131:       @translator ||= Translator.new
132:     end
type_translation()

Returns true if type translation is enabled for this database, or false otherwise.

     # File lib/sqlite/database.rb, line 136
136:     def type_translation
137:       @type_translation
138:     end
type_translation=( mode )

Enable or disable type translation for this database.

     # File lib/sqlite/database.rb, line 141
141:     def type_translation=( mode )
142:       @type_translation = mode
143:     end

[Validate]