class SQLite3::Database
The Database class encapsulates a single connection to a SQLite3 database. Its usage is very straightforward:
require 'sqlite3' SQLite3::Database.new( "data.db" ) do |db| db.execute( "select * from table" ) do |row| p row end end
It wraps the lower-level methods provides by the selected driver, and includes the Pragmas module for access to various pragma convenience methods.
The Database class provides type translation services as well, by which the SQLite3 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
A reference to the underlying SQLite3 driver used by this database.
The low-level opaque database handle that this object wraps.
A boolean that indicates whether rows in result sets should be returned as hashes or not. By default, rows are returned as arrays.
A boolean indicating whether or not type translation is enabled for this database.
Public Class Methods
Create a new Database object that opens the
given file. If utf16 is true
, the filename is interpreted as a
UTF-16 encoded string.
By default, the new database will return result rows as arrays (#results_as_hash) and has type translation disabled (#type_translation=).
# File lib/sqlite3/database.rb, line 70 def initialize( file_name, options={} ) # :yields: db utf16 = options.fetch(:utf16, false) load_driver( options[:driver] ) @statement_factory = options[:statement_factory] || Statement result, @handle = @driver.open( file_name, utf16 ) Error.check( result, self, "could not open database" ) @closed = false @results_as_hash = options.fetch(:results_as_hash,false) @type_translation = options.fetch(:type_translation,false) @translator = nil @transaction_active = false if block_given? begin yield self ensure self.close end end end
Public Instance Methods
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 the mutually exclusive busy_timeout.
# File lib/sqlite3/database.rb, line 315 def busy_handler( data=nil, &block ) # :yields: data, retries result = @driver.busy_handler( @handle, data, &block ) Error.check( result, self ) end
Indicates that if a request for a resource terminates because that resource
is busy, SQLite should sleep and retry for up to the indicated number of
milliseconds. By default, SQLite does not retry busy resources. To restore
the default behavior, send 0 as the ms
parameter.
See also the mutually exclusive busy_handler.
# File lib/sqlite3/database.rb, line 327 def busy_timeout( ms ) result = @driver.busy_timeout( @handle, ms ) Error.check( result, self ) end
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/sqlite3/database.rb, line 291 def changes @driver.changes( @handle ) end
Closes this database.
# File lib/sqlite3/database.rb, line 124 def close unless @closed result = @driver.close( @handle ) Error.check( result, self ) end @closed = true end
Returns true
if this database instance has been closed (see close).
# File lib/sqlite3/database.rb, line 133 def closed? @closed end
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/sqlite3/database.rb, line 586 def commit execute "commit transaction" @transaction_active = false true end
Return true
if the string is a valid (ie, parsable) SQL
statement, and false
otherwise. If utf16
is
true
, then the string is a UTF-16 character string.
# File lib/sqlite3/database.rb, line 97 def complete?( string, utf16=false ) @driver.complete?( string, utf16 ) end
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.)
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 SQLite3::Database::FunctionProxy#set_result
to store the result of the function.
Example:
db.create_aggregate( "lengths", 1 ) do step do |func, value| func[ :total ] ||= 0 func[ :total ] += ( value ? value.length : 0 ) end finalize do |func| func.set_result( func[ :total ] || 0 ) end end 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/sqlite3/database.rb, line 411 def create_aggregate( name, arity, step=nil, finalize=nil, text_rep=Constants::TextRep::ANY, &block ) # begin if block proxy = AggregateDefinitionProxy.new proxy.instance_eval(&block) step ||= proxy.step_callback finalize ||= proxy.finalize_callback end step_callback = proc do |func,*args| ctx = @driver.aggregate_context( func ) unless ctx[:__error] begin step.call( FunctionProxy.new( @driver, func, ctx ), *args.map{|v| Value.new(self,v)} ) rescue Exception => e ctx[:__error] = e end end end finalize_callback = proc do |func| ctx = @driver.aggregate_context( func ) unless ctx[:__error] begin finalize.call( FunctionProxy.new( @driver, func, ctx ) ) rescue Exception => e @driver.result_error( func, "#{e.message} (#{e.class})", -1 ) end else e = ctx[:__error] @driver.result_error( func, "#{e.message} (#{e.class})", -1 ) end end result = @driver.create_function( @handle, name, arity, text_rep, nil, nil, step_callback, finalize_callback ) Error.check( result, self ) self end
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:
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.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/sqlite3/database.rb, line 502 def create_aggregate_handler( handler ) arity = -1 text_rep = Constants::TextRep::ANY arity = handler.arity if handler.respond_to?(:arity) text_rep = handler.text_rep if handler.respond_to?(:text_rep) name = handler.name step = proc do |func,*args| ctx = @driver.aggregate_context( func ) unless ctx[ :__error ] ctx[ :handler ] ||= handler.new begin ctx[ :handler ].step( FunctionProxy.new( @driver, func, ctx ), *args.map{|v| Value.new(self,v)} ) rescue Exception, StandardError => e ctx[ :__error ] = e end end end finalize = proc do |func| ctx = @driver.aggregate_context( func ) unless ctx[ :__error ] ctx[ :handler ] ||= handler.new begin ctx[ :handler ].finalize( FunctionProxy.new( @driver, func, ctx ) ) rescue Exception => e ctx[ :__error ] = e end end if ctx[ :__error ] e = ctx[ :__error ] @driver.sqlite3_result_error( func, "#{e.message} (#{e.class})", -1 ) end end result = @driver.create_function( @handle, name, arity, text_rep, nil, nil, step, finalize ) Error.check( result, self ) self end
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.)
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 SQLite3::Database::FunctionProxy#set_result
method on the func
parameter and indicate the return value
that way.
Example:
db.create_function( "maim", 1 ) do |func, value| if value.nil? func.result = nil else func.result = value.split(//).sort.join end end puts db.get_first_value( "select maim(name) from table" )
# File lib/sqlite3/database.rb, line 355 def create_function( name, arity, text_rep=Constants::TextRep::ANY, &block ) # :yields: func, *args # begin callback = proc do |func,*args| begin block.call( FunctionProxy.new( @driver, func ), *args.map{|v| Value.new(self,v)} ) rescue StandardError, Exception => e @driver.result_error( func, "#{e.message} (#{e.class})", -1 ) end end result = @driver.create_function( @handle, name, arity, text_rep, nil, callback, nil, nil ) Error.check( result, self ) self end
Return an integer representing the last error to have occurred with this database.
# File lib/sqlite3/database.rb, line 109 def errcode @driver.errcode( @handle ) end
Return a string describing the last error to have occurred with this database.
# File lib/sqlite3/database.rb, line 103 def errmsg( utf16=false ) @driver.errmsg( @handle, utf16 ) end
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.
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, query, and execute_batch for additional ways of executing statements.
# File lib/sqlite3/database.rb, line 186 def execute( sql, *bind_vars ) prepare( sql ) do |stmt| result = stmt.execute( *bind_vars ) if block_given? result.each { |row| yield row } else return result.inject( [] ) { |arr,row| arr << row; arr } end end end
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, query, and execute_batch for additional ways of executing statements.
# File lib/sqlite3/database.rb, line 207 def execute2( sql, *bind_vars ) prepare( sql ) do |stmt| result = stmt.execute( *bind_vars ) if block_given? yield result.columns result.each { |row| yield row } else return result.inject( [ result.columns ] ) { |arr,row| arr << row; arr } end end end
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/sqlite3/database.rb, line 228 def execute_batch( sql, *bind_vars ) sql = sql.strip until sql.empty? do prepare( sql ) do |stmt| stmt.execute( *bind_vars ) sql = stmt.remainder.strip end end nil end
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/sqlite3/database.rb, line 267 def get_first_row( sql, *bind_vars ) execute( sql, *bind_vars ) { |row| return row } nil end
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/sqlite3/database.rb, line 277 def get_first_value( sql, *bind_vars ) execute( sql, *bind_vars ) { |row| return row[0] } nil end
Interrupts the currently executing operation, causing it to abort.
# File lib/sqlite3/database.rb, line 302 def interrupt @driver.interrupt( @handle ) end
Obtains the unique row ID of the last row to be inserted by this Database instance.
# File lib/sqlite3/database.rb, line 284 def last_insert_row_id @driver.last_insert_rowid( @handle ) end
Returns a Statement object representing the given SQL. This does not execute the statement; it merely prepares the statement for execution.
The Statement can then be executed using Statement#execute.
# File lib/sqlite3/database.rb, line 159 def prepare( sql ) stmt = @statement_factory.new( self, sql ) if block_given? begin yield stmt ensure stmt.close end else return stmt end end
This is a convenience method for creating a statement, binding paramters to it, and calling execute:
result = db.query( "select * from foo where a=?", 5 ) # is the same as result = db.prepare( "select * from foo where a=?" ).execute( 5 )
You must be sure to call close
on the ResultSet instance that is returned, or you could
have problems with locks on the table. If called with a block,
close
will be invoked implicitly when the block terminates.
# File lib/sqlite3/database.rb, line 250 def query( sql, *bind_vars ) result = prepare( sql ).execute( *bind_vars ) if block_given? begin yield result ensure result.close end else return result end end
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/sqlite3/database.rb, line 45 def quote( string ) string.gsub( /'/, "''" ) end
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/sqlite3/database.rb, line 596 def rollback execute "rollback transaction" @transaction_active = false true end
Returns the total number of changes made to this database instance since it was opened.
# File lib/sqlite3/database.rb, line 297 def total_changes @driver.total_changes( @handle ) end
Installs (or removes) a block that will be invoked for every SQL statement
executed. The block receives a two parameters: the data
argument, and the SQL statement executed. If the block is nil
,
any existing tracer will be uninstalled.
# File lib/sqlite3/database.rb, line 141 def trace( data=nil, &block ) @driver.trace( @handle, data, &block ) end
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.
The mode
parameter may be either :deferred
(the
default), :immediate
, or :exclusive
.
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/sqlite3/database.rb, line 563 def transaction( mode = :deferred ) execute "begin #{mode.to_s} transaction" @transaction_active = true if block_given? abort = false begin yield self rescue ::Object abort = true raise ensure abort and rollback or commit end end true end
Returns true
if there is a transaction active, and
false
otherwise.
# File lib/sqlite3/database.rb, line 603 def transaction_active? @transaction_active end
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/sqlite3/database.rb, line 119 def translator @translator ||= Translator.new end