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_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.

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