Class: SQLite::Database

Class SQLite::Database |
In: | lib/sqlite/database.rb
Parent: | Object

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

- busy_handler
- busy_timeout
- changes
- close
- closed?
- commit
- complete?
- create_aggregate
- create_aggregate_handler
- create_function
- decode
- encode
- execute
- execute2
- execute_batch
- get_first_row
- get_first_value
- interrupt
- last_insert_row_id
- new
- open
- prepare
- query
- quote
- rollback
- transaction
- transaction_active?
- translator
- type_translation
- type_translation=

Included Modules

- SQLite::Pragmas

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.

[ show source ]

         # 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.

[ show source ]

        # 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.

[ show source ]

        # 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=).

[ show source ]

         # 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.

[ show source ]

        # 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.

[ show source ]

        # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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).

[ show source ]

         # 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`.

[ show source ]

         # 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.

[ show source ]

         # 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" )

[ show source ]

         # 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" )

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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`.

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

         # 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.)

[ show source ]

         # 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.

[ show source ]

         # 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.

[ show source ]

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

[Validate]