Class: SQLite::Database

### Home Classes Methods

### In Files

- lib/sqlite/database.rb

### Parent

Object

### Namespace

- CLASS SQLite::Database::FunctionProxy

### Methods

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

### Included Modules

- SQLite::Pragmas

### Files

- README

### Class/Module Index

Quicksearch

- SQLite
- SQLite::API
- SQLite::Database
- SQLite::Database::FunctionProxy
- SQLite::Exceptions
- SQLite::Exceptions::AbortException
- SQLite::Exceptions::AuthorizationException
- SQLite::Exceptions::BusyException
- SQLite::Exceptions::CantOpenException
- SQLite::Exceptions::ConstraintException
- SQLite::Exceptions::CorruptException
- SQLite::Exceptions::DatabaseException
- SQLite::Exceptions::EmptyException
- SQLite::Exceptions::FormatException
- SQLite::Exceptions::FullException
- SQLite::Exceptions::IOErrorException
- SQLite::Exceptions::InternalException
- SQLite::Exceptions::InterruptException
- SQLite::Exceptions::LockedException
- SQLite::Exceptions::MismatchException
- SQLite::Exceptions::MisuseException
- SQLite::Exceptions::NotADatabaseException
- SQLite::Exceptions::NotFoundException
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- SQLite::Exceptions::PermissionsException
- SQLite::Exceptions::ProtocolException
- SQLite::Exceptions::RangeException
- SQLite::Exceptions::ReadOnlyException
- SQLite::Exceptions::SQLException
- SQLite::Exceptions::SchemaChangedException
- SQLite::Exceptions::TooBigException
- SQLite::Exceptions::UnsupportedOSFeatureException
- SQLite::ParsedStatement
- SQLite::Pragmas
- SQLite::ResultSet
- SQLite::ResultSet::FieldsContainer
- SQLite::ResultSet::TypesContainer
- SQLite::Statement
- SQLite::Translator
- SQLite::Version

No matching classes.

# SQLite::Database

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.

### Attributes

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.

### Public Class Methods

complete?( string ) click to toggle source

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

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

decode( string ) click to toggle source

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
    def self.decode( string )
      Marshal.load( Base64.decode64( string ) )
    end

encode( object ) click to toggle source

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
    def self.encode( object )
      Base64.encode64( Marshal.dump( object ) ).strip
    end

new( file_name, mode=0 ) click to toggle source

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
    def initialize( file_name, mode=0 )
      @handle = SQLite::API.open( file_name, mode )
      @closed = false
      @results_as_hash = false
      @type_translation = false
      @translator = nil
    end

open( file_name ) click to toggle source

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
    def self.open( file_name )
      new( file_name, 0 )
    end

quote( string ) click to toggle source

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
    def self.quote( string )
      string.gsub( /'/, "''" )
    end

### Public Instance Methods

busy_handler( ) click to toggle source

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
    def busy_handler( &block ) # :yields: resource, retries
      SQLite::API.busy_handler( @handle, block )
    end

busy_timeout( ms ) click to toggle source

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
    def busy_timeout( ms )
      SQLite::API.busy_timeout( @handle, ms )
    end

changes() click to toggle source

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
    def changes
      SQLite::API.changes( @handle )
    end

close() click to toggle source

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
    def close
      SQLite::API.close( @handle )
      @closed = true
    end

closed?() click to toggle source

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

    # File lib/sqlite/database.rb, line 154
    def closed?
      @closed
    end

commit() click to toggle source

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
    def commit
      execute "commit transaction"
      @transaction_active = false
      true
    end

create_aggregate( name, arity, step, finalize, type=nil ) click to toggle source

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
    def create_aggregate( name, arity, step, finalize, type=nil )
      case type
        when :numeric
          type = SQLite::API::NUMERIC
        when :text
          type = SQLite::API::TEXT
        when :args
          type = SQLite::API::ARGS
      end

      step_callback = proc do |func,*args|
        ctx = SQLite::API.aggregate_context( func )
        unless ctx[:__error]
          begin
            step.call( FunctionProxy.new( func, ctx ), *args )
          rescue Exception => e
            ctx[:__error] = e
          end
        end
      end

      finalize_callback = proc do |func|
        ctx = SQLite::API.aggregate_context( func )
        unless ctx[:__error]
          begin
            finalize.call( FunctionProxy.new( func, ctx ) )
          rescue Exception => e
            SQLite::API.set_result_error( func, "#{e.message} (#{e.class})" )
          end
        else
          e = ctx[:__error]
          SQLite::API.set_result_error( func, "#{e.message} (#{e.class})" )
        end
      end

      SQLite::API.create_aggregate( @handle, name, arity,
        step_callback, finalize_callback )

      SQLite::API.function_type( @handle, name, type ) if type

      self
    end

create_aggregate_handler( handler ) click to toggle source

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
    def create_aggregate_handler( handler )
      type = nil
      arity = -1

      type = handler.function_type if handler.respond_to?(:function_type)
      arity = handler.arity if handler.respond_to?(:arity)
      name = handler.name

      case type
        when :numeric
          type = SQLite::API::NUMERIC
        when :text
          type = SQLite::API::TEXT
        when :args
          type = SQLite::API::ARGS
      end

      step = proc do |func,*args|
        ctx = SQLite::API.aggregate_context( func )
        unless ctx[ :__error ]
          ctx[ :handler ] ||= handler.new
          begin
            ctx[ :handler ].step( FunctionProxy.new( func, ctx ), *args )
          rescue Exception => e
            ctx[ :__error ] = e
          end
        end
      end

      finalize = proc do |func|
        ctx = SQLite::API.aggregate_context( func )
        unless ctx[ :__error ]
          ctx[ :handler ] ||= handler.new
          begin
            ctx[ :handler ].finalize( FunctionProxy.new( func, ctx ) )
          rescue Exception => e
            ctx[ :__error ] = e
          end
        end

        if ctx[ :__error ]
          e = ctx[ :__error ]
          SQLite::API.set_result_error( func, "#{e.message} (#{e.class})" )
        end
      end

      SQLite::API.create_aggregate( @handle, name, arity, step, finalize )
      SQLite::API.function_type( @handle, name, type ) if type

      self
    end

create_function( name, arity, type=nil ) click to toggle source

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
    def create_function( name, arity, type=nil, &block ) # :yields: func, *args
      case type
        when :numeric
          type = SQLite::API::NUMERIC
        when :text
          type = SQLite::API::TEXT
        when :args
          type = SQLite::API::ARGS
      end

      callback = proc do |func,*args|
        begin
          block.call( FunctionProxy.new( func ), *args )
        rescue Exception => e
          SQLite::API.set_result_error( func, "#{e.message} (#{e.class})" )
        end
      end

      SQLite::API.create_function( @handle, name, arity, callback )
      SQLite::API.function_type( @handle, name, type ) if type

      self
    end

execute( sql, *bind_vars ) click to toggle source

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
    def execute( sql, *bind_vars )
      stmt = prepare( sql )
      stmt.bind_params( *bind_vars )
      result = stmt.execute
      begin
        if block_given?
          result.each { |row| yield row }
        else
          return result.inject( [] ) { |arr,row| arr << row; arr }
        end
      ensure
        result.close
      end
    end

execute2( sql, *bind_vars ) click to toggle source

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
    def execute2( sql, *bind_vars )
      stmt = prepare( sql )
      stmt.bind_params( *bind_vars )
      result = stmt.execute
      begin
        if block_given?
          yield result.columns
          result.each { |row| yield row }
        else
          return result.inject( [ result.columns ] ) { |arr,row| arr << row; arr }
        end
      ensure
        result.close
      end
    end

execute_batch( sql, *bind_vars ) click to toggle source

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
    def execute_batch( sql, *bind_vars )
      loop do
        stmt = prepare( sql )
        stmt.bind_params *bind_vars
        stmt.execute
        sql = stmt.remainder
        break if sql.length < 1
      end
      nil
    end

get_first_row( sql, *bind_vars ) click to toggle source

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
    def get_first_row( sql, *bind_vars )
      execute( sql, *bind_vars ) { |row| return row }
      nil
    end

get_first_value( sql, *bind_vars ) click to toggle source

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
    def get_first_value( sql, *bind_vars )
      execute( sql, *bind_vars ) { |row| return row[0] }
      nil
    end

interrupt() click to toggle source

Interrupts the currently executing operation, causing it to abort.

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

last_insert_row_id() click to toggle source

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

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

prepare( sql ) click to toggle source

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
    def prepare( sql )
      Statement.new( self, sql )
    end

query( sql, *bind_vars ) click to toggle source

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
    def query( sql, *bind_vars, &block ) # :yields: result_set
      stmt = prepare( sql )
      stmt.bind_params( *bind_vars )
      stmt.execute( &block )
    end

rollback() click to toggle source

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
    def rollback
      execute "rollback transaction"
      @transaction_active = false
      true
    end

transaction() click to toggle source

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
    def transaction
      execute "begin transaction"
      @transaction_active = true

      if block_given?
        abort = false
        begin
          yield self
        rescue Exception
          abort = true
          raise
        ensure
          abort and rollback or commit
        end
      end

      true
    end

transaction_active?() click to toggle source

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

    # File lib/sqlite/database.rb, line 610
    def transaction_active?
      @transaction_active
    end

translator() click to toggle source

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
    def translator
      @translator ||= Translator.new
    end

type_translation() click to toggle source

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

    # File lib/sqlite/database.rb, line 136
    def type_translation
      @type_translation
    end

type_translation=( mode ) click to toggle source

Enable or disable type translation for this database.

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

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