Class | SQLite3::Database |
In: |
lib/sqlite3/database.rb
|
Parent: | Object |
The Database class encapsulates a single connection to a SQLite3 database. Its usage is very straightforward:
require 'sqlite3' db = SQLite3::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 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.
new | -> | open |
driver | [R] | A reference to the underlying SQLite3 driver used by this database. |
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. |
type_translation | [RW] | A boolean indicating whether or not type translation is enabled for this database. |
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 105 105: def initialize( file_name, options={} ) 106: utf16 = options.fetch(:utf16, false) 107: load_driver( options[:driver] ) 108: 109: @statement_factory = options[:statement_factory] || Statement 110: 111: result, @handle = @driver.open( file_name, utf16 ) 112: Error.check( result, self, "could not open database" ) 113: 114: @closed = false 115: @results_as_hash = options.fetch(:results_as_hash,false) 116: @type_translation = options.fetch(:type_translation,false) 117: @translator = nil 118: @transaction_active = false 119: 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 80 80: def quote( string ) 81: string.gsub( /'/, "''" ) 82: end
Installs (or removes) a block that will be invoked for every access to the database. If the block returns 0 (or nil), the statement is allowed to proceed. Returning 1 causes an authorization error to occur, and returning 2 causes the access to be silently denied.
# File lib/sqlite3/database.rb, line 176 176: def authorizer( data=nil, &block ) 177: result = @driver.set_authorizer( @handle, data, &block ) 178: Error.check( result, self ) 179: end
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/sqlite3/database.rb, line 339 339: def busy_handler( data=nil, &block ) # :yields: data, retries 340: result = @driver.busy_handler( @handle, data, &block ) 341: Error.check( result, self ) 342: end
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/sqlite3/database.rb, line 351 351: def busy_timeout( ms ) 352: result = @driver.busy_timeout( @handle, ms ) 353: Error.check( result, self ) 354: 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 315 315: def changes 316: @driver.changes( @handle ) 317: end
Closes this database.
# File lib/sqlite3/database.rb, line 151 151: def close 152: unless @closed 153: result = @driver.close( @handle ) 154: Error.check( result, self ) 155: end 156: @closed = true 157: 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 610 610: def commit 611: execute "commit transaction" 612: @transaction_active = false 613: true 614: 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 124 124: def complete?( string, utf16=false ) 125: @driver.complete?( string, utf16 ) 126: 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 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 435 435: def create_aggregate( name, arity, step=nil, finalize=nil, 436: text_rep=Constants::TextRep::ANY, &block ) 437: # begin 438: if block 439: proxy = AggregateDefinitionProxy.new 440: proxy.instance_eval(&block) 441: step ||= proxy.step_callback 442: finalize ||= proxy.finalize_callback 443: end 444: 445: step_callback = proc do |func,*args| 446: ctx = @driver.aggregate_context( func ) 447: unless ctx[:__error] 448: begin 449: step.call( FunctionProxy.new( @driver, func, ctx ), 450: *args.map{|v| Value.new(self,v)} ) 451: rescue Exception => e 452: ctx[:__error] = e 453: end 454: end 455: end 456: 457: finalize_callback = proc do |func| 458: ctx = @driver.aggregate_context( func ) 459: unless ctx[:__error] 460: begin 461: finalize.call( FunctionProxy.new( @driver, func, ctx ) ) 462: rescue Exception => e 463: @driver.result_error( func, 464: "#{e.message} (#{e.class})", -1 ) 465: end 466: else 467: e = ctx[:__error] 468: @driver.result_error( func, 469: "#{e.message} (#{e.class})", -1 ) 470: end 471: end 472: 473: result = @driver.create_function( @handle, name, arity, text_rep, nil, 474: nil, step_callback, finalize_callback ) 475: Error.check( result, self ) 476: 477: self 478: 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 526 526: def create_aggregate_handler( handler ) 527: arity = -1 528: text_rep = Constants::TextRep::ANY 529: 530: arity = handler.arity if handler.respond_to?(:arity) 531: text_rep = handler.text_rep if handler.respond_to?(:text_rep) 532: name = handler.name 533: 534: step = proc do |func,*args| 535: ctx = @driver.aggregate_context( func ) 536: unless ctx[ :__error ] 537: ctx[ :handler ] ||= handler.new 538: begin 539: ctx[ :handler ].step( FunctionProxy.new( @driver, func, ctx ), 540: *args.map{|v| Value.new(self,v)} ) 541: rescue Exception, StandardError => e 542: ctx[ :__error ] = e 543: end 544: end 545: end 546: 547: finalize = proc do |func| 548: ctx = @driver.aggregate_context( func ) 549: unless ctx[ :__error ] 550: ctx[ :handler ] ||= handler.new 551: begin 552: ctx[ :handler ].finalize( FunctionProxy.new( @driver, func, ctx ) ) 553: rescue Exception => e 554: ctx[ :__error ] = e 555: end 556: end 557: 558: if ctx[ :__error ] 559: e = ctx[ :__error ] 560: @driver.sqlite3_result_error( func, "#{e.message} (#{e.class})", -1 ) 561: end 562: end 563: 564: result = @driver.create_function( @handle, name, arity, text_rep, nil, 565: nil, step, finalize ) 566: Error.check( result, self ) 567: 568: self 569: 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 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 379 379: def create_function( name, arity, text_rep=Constants::TextRep::ANY, 380: &block ) # :yields: func, *args 381: # begin 382: callback = proc do |func,*args| 383: begin 384: block.call( FunctionProxy.new( @driver, func ), 385: *args.map{|v| Value.new(self,v)} ) 386: rescue StandardError, Exception => e 387: @driver.result_error( func, 388: "#{e.message} (#{e.class})", -1 ) 389: end 390: end 391: 392: result = @driver.create_function( @handle, name, arity, text_rep, nil, 393: callback, nil, nil ) 394: Error.check( result, self ) 395: 396: self 397: end
Return an integer representing the last error to have occurred with this database.
# File lib/sqlite3/database.rb, line 136 136: def errcode 137: @driver.errcode( @handle ) 138: end
Return a string describing the last error to have occurred with this database.
# File lib/sqlite3/database.rb, line 130 130: def errmsg( utf16=false ) 131: @driver.errmsg( @handle, utf16 ) 132: 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 210 210: def execute( sql, *bind_vars ) 211: prepare( sql ) do |stmt| 212: result = stmt.execute( *bind_vars ) 213: if block_given? 214: result.each { |row| yield row } 215: else 216: return result.inject( [] ) { |arr,row| arr << row; arr } 217: end 218: end 219: 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 231 231: def execute2( sql, *bind_vars ) 232: prepare( sql ) do |stmt| 233: result = stmt.execute( *bind_vars ) 234: if block_given? 235: yield result.columns 236: result.each { |row| yield row } 237: else 238: return result.inject( [ result.columns ] ) { |arr,row| 239: arr << row; arr } 240: end 241: end 242: 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 252 252: def execute_batch( sql, *bind_vars ) 253: sql = sql.strip 254: until sql.empty? do 255: prepare( sql ) do |stmt| 256: stmt.execute( *bind_vars ) 257: sql = stmt.remainder.strip 258: end 259: end 260: nil 261: 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 291 291: def get_first_row( sql, *bind_vars ) 292: execute( sql, *bind_vars ) { |row| return row } 293: nil 294: 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 301 301: def get_first_value( sql, *bind_vars ) 302: execute( sql, *bind_vars ) { |row| return row[0] } 303: nil 304: end
Interrupts the currently executing operation, causing it to abort.
# File lib/sqlite3/database.rb, line 326 326: def interrupt 327: @driver.interrupt( @handle ) 328: end
Returns a Statement object representing the given SQL. This does not execute the statement; it merely prepares the statement for execution.
# File lib/sqlite3/database.rb, line 183 183: def prepare( sql ) 184: stmt = @statement_factory.new( self, sql ) 185: if block_given? 186: begin 187: yield stmt 188: ensure 189: stmt.close 190: end 191: else 192: return stmt 193: end 194: 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 274 274: def query( sql, *bind_vars ) 275: result = prepare( sql ).execute( *bind_vars ) 276: if block_given? 277: begin 278: yield result 279: ensure 280: result.close 281: end 282: else 283: return result 284: end 285: 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 620 620: def rollback 621: execute "rollback transaction" 622: @transaction_active = false 623: true 624: end
Returns the total number of changes made to this database instance since it was opened.
# File lib/sqlite3/database.rb, line 321 321: def total_changes 322: @driver.total_changes( @handle ) 323: 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 168 168: def trace( data=nil, &block ) 169: @driver.trace( @handle, data, &block ) 170: 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 587 587: def transaction( mode = :deferred ) 588: execute "begin #{mode.to_s} transaction" 589: @transaction_active = true 590: 591: if block_given? 592: abort = false 593: begin 594: yield self 595: rescue ::Object 596: abort = true 597: raise 598: ensure 599: abort and rollback or commit 600: end 601: end 602: 603: true 604: end
Returns true if there is a transaction active, and false otherwise.
# File lib/sqlite3/database.rb, line 627 627: def transaction_active? 628: @transaction_active 629: 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 146 146: def translator 147: @translator ||= Translator.new 148: end