Class: SQLite3::Database

Inherits:
Object
  • Object
show all
Includes:
Pragmas
Defined in:
lib/sqlite3/database.rb

Overview

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.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Pragmas

#table_info

Constructor Details

#initialize(file_name, options = {}) ⇒ 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=).



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# File 'lib/sqlite3/database.rb', line 68

def initialize(file_name, options = {})
  @encoding = Encoding.find(options.fetch(:encoding, "utf-8"))

  load_driver(options[:driver])

  @statement_factory = options[:statement_factory] || Statement

  result, @handle = @driver.open(file_name, Encoding.utf_16?(@encoding))
  Error.check(result, self, "could not open database")

  @closed = false
  @results_as_hash = options.fetch(:results_as_hash, false)
end

Instance Attribute Details

#driver ⇒ Object (readonly)

A reference to the underlying SQLite3 driver used by this database.



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# File 'lib/sqlite3/database.rb', line 50

def driver
  @driver
end

#encoding ⇒ Object (readonly)

Encoding used to comunicate with database.



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# File 'lib/sqlite3/database.rb', line 61

def encoding
  @encoding
end

#handle ⇒ Object (readonly)

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



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# File 'lib/sqlite3/database.rb', line 47

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/sqlite3/database.rb', line 54

def results_as_hash
  @results_as_hash
end

Class Method Details

.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/sqlite3/database.rb', line 40

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

Instance Method Details

#busy_timeout(ms) ⇒ Object

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.



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# File 'lib/sqlite3/database.rb', line 218

def busy_timeout(ms)
  result = @driver.busy_timeout(@handle, ms)
  Error.check(result, self)
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/sqlite3/database.rb', line 207

def changes
  @driver.changes(@handle)
end

#close ⇒ Object

Closes this database.



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# File 'lib/sqlite3/database.rb', line 101

def close
  unless @closed
    result = @driver.close(@handle)
    Error.check(result, self)
  end
  @closed = true
end

#closed? ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/sqlite3/database.rb', line 110

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/sqlite3/database.rb', line 262

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

#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/sqlite3/database.rb', line 84

def complete?(string)
  @driver.complete?(string)
end

#errcode ⇒ Object

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



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# File 'lib/sqlite3/database.rb', line 96

def errcode
  @driver.errcode(@handle)
end

#errmsg ⇒ Object

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



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# File 'lib/sqlite3/database.rb', line 90

def errmsg
  @driver.errmsg(@handle)
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.

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.



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# File 'lib/sqlite3/database.rb', line 146

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

#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, #query, and #execute_batch for additional ways of executing statements.



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# File 'lib/sqlite3/database.rb', line 167

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

#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/sqlite3/database.rb', line 183

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/sqlite3/database.rb', line 193

def get_first_value(sql, *bind_vars)
  execute(sql, *bind_vars) { |row| return row[0] }
  nil
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/sqlite3/database.rb', line 200

def last_insert_row_id
  @driver.last_insert_rowid(@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.

The Statement can then be executed using Statement#execute.



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# File 'lib/sqlite3/database.rb', line 119

def prepare(sql)
  stmt = @statement_factory.new(self, sql, Encoding.utf_16?(@encoding))
  if block_given?
    begin
      yield stmt
    ensure
      stmt.close
    end
  else
    return stmt
  end
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/sqlite3/database.rb', line 272

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

#transaction(mode = :deferred) ⇒ 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.

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.



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# File 'lib/sqlite3/database.rb', line 239

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

#transaction_active? ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/sqlite3/database.rb', line 279

def transaction_active?
  @transaction_active
end