Class: SQLite::Database

Inherits:
Object
  • Object
show all
Includes:
Pragmas
Defined in:
lib/sqlite/database.rb

Overview

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.

Defined Under Namespace

Classes: FunctionProxy

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(file_name, mode = 0) ⇒ Database

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=).



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# 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

Instance Attribute Details

#handle ⇒ Object (readonly)

The low-level opaque database handle that this object wraps.



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# File 'lib/sqlite/database.rb', line 104

def handle
  @handle
end

#results_as_hash ⇒ Object

A boolean that indicates whether rows in result sets should be returned as hashes or not. By default, rows are returned as arrays.



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# File 'lib/sqlite/database.rb', line 108

def results_as_hash
  @results_as_hash
end

Class Method Details

.complete?(string) ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/sqlite/database.rb', line 99

def self.complete?( string )
  SQLite::API.complete( string )
end

.decode(string) ⇒ Object

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



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# File 'lib/sqlite/database.rb', line 93

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

.encode(object) ⇒ Object

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



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# File 'lib/sqlite/database.rb', line 87

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

.open(file_name) ⇒ Object

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



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# File 'lib/sqlite/database.rb', line 74

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

.quote(string) ⇒ Object

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.



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# File 'lib/sqlite/database.rb', line 81

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

Instance Method Details

#busy_handler(&block) ⇒ Object

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.



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# File 'lib/sqlite/database.rb', line 307

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

#busy_timeout(ms) ⇒ Object

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.



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# File 'lib/sqlite/database.rb', line 318

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

#changes ⇒ Object

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.



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# File 'lib/sqlite/database.rb', line 289

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

#close ⇒ Object

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.



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# File 'lib/sqlite/database.rb', line 148

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

#closed? ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/sqlite/database.rb', line 154

def closed?
  @closed
end

#commit ⇒ Object

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.



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# 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) ⇒ Object

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.



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# 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) ⇒ Object

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" )



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# 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, &block) ⇒ Object

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" )



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# 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) ⇒ Object

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.



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# 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) ⇒ Object

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.



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# 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) ⇒ Object

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.



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# 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) ⇒ Object

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.



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# 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) ⇒ Object

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.



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# 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 ⇒ Object

Interrupts the currently executing operation, causing it to abort.



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# File 'lib/sqlite/database.rb', line 294

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

#last_insert_row_id ⇒ Object

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



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# File 'lib/sqlite/database.rb', line 282

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

#prepare(sql) ⇒ Object

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



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# File 'lib/sqlite/database.rb', line 160

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

#query(sql, *bind_vars, &block) ⇒ Object

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.



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# 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 ⇒ Object

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.



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# File 'lib/sqlite/database.rb', line 603

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

#transaction ⇒ Object

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.



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# 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? ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/sqlite/database.rb', line 610

def transaction_active?
  @transaction_active
end

#translator ⇒ Object

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.)



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# File 'lib/sqlite/database.rb', line 130

def translator
  @translator ||= Translator.new
end

#type_translation ⇒ Object

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



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# File 'lib/sqlite/database.rb', line 136

def type_translation
  @type_translation
end

#type_translation=(mode) ⇒ Object

Enable or disable type translation for this database.



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# File 'lib/sqlite/database.rb', line 141

def type_translation=( mode )
  @type_translation = mode
end