Class: SQLite3::Database

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.

### Methods

authorizer busy_handler busy_timeout changes close closed? commit complete? create_aggregate create_aggregate_handler create_function errcode errmsg execute execute2 execute_batch get_first_row get_first_value interrupt last_insert_row_id new prepare query quote rollback total_changes trace transaction transaction_active? translator

### Included Modules

Pragmas

### Classes and Modules

Class SQLite3::Database::FunctionProxy

### External Aliases

new | -> | open

### Attributes

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.

### Public Class methods

new( file_name, options={} )

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=).

quote( string )

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.

### Public Instance methods

authorizer( data=nil, &block )

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.

busy_handler( data=nil ) {|data, retries| ...}

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.

busy_timeout( ms )

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.

changes()

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.

close()

Closes this database.

closed?()

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

commit()

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`.

complete?( string, utf16=false )

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.

create_aggregate( name, arity, step=nil, finalize=nil, text_rep=Constants::TextRep::ANY, &block )

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.

create_aggregate_handler( handler )

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" )

create_function( name, arity, text_rep=Constants::TextRep::ANY ) {|func, *args| ...}

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" )

errcode()

Return an integer representing the last error to have occurred with this database.

errmsg( utf16=false )

Return a string describing the last error to have occurred with this database.

execute( sql, *bind_vars ) {|row| ...}

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.

execute2( sql, *bind_vars ) {|result.columns| ...}

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.

execute_batch( sql, *bind_vars )

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.

get_first_row( sql, *bind_vars )

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.

get_first_value( sql, *bind_vars )

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.

interrupt()

Interrupts the currently executing operation, causing it to abort.

last_insert_row_id()

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

prepare( sql ) {|stmt| ...}

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.

query( sql, *bind_vars ) {|result| ...}

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.

rollback()

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`.

total_changes()

Returns the total number of changes made to this database instance since it was opened.

trace( data=nil, &block )

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.

transaction( mode = :deferred ) {|self| ...}

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.

transaction_active?()

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

translator()

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.)

[Validate]