Example — APSW 3.8.11.1-r1 documentation

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# Example

This code demonstrates usage of the APSW api. It gives you a good overview of all the things that can be done. Also included is output so you can see what gets printed when you run the code.

    import os, sys, time
    import apsw

    ###
    ### Check we have the expected version of apsw and sqlite
    ###

    print "      Using APSW file",apsw.__file__                # from the extension module
    print "         APSW version",apsw.apswversion()           # from the extension module
    print "   SQLite lib version",apsw.sqlitelibversion()      # from the sqlite library code
    print "SQLite header version",apsw.SQLITE_VERSION_NUMBER   # from the sqlite header file at compile time

    |       Using APSW file /space/apsw/apsw.so
    |          APSW version 3.8.11.1-r1
    |    SQLite lib version 3.8.11.1
    | SQLite header version 3008011

    ###
    ### Opening/creating database
    ###

    connection=apsw.Connection("dbfile")
    cursor=connection.cursor()

    ###
    ### simple statement
    ###

    cursor.execute("create table foo(x,y,z)")

    ###
    ### using different types
    ###

    cursor.execute("insert into foo values(?,?,?)", (1, 1.1, None))  # integer, float/real, Null
    cursor.execute("insert into foo(x) values(?)", ("abc", ))        # string (note trailing comma to ensure tuple!)
    cursor.execute("insert into foo(x) values(?)",                   # a blob (binary data)
                        (buffer("abc\xff\xfe"), ))                   # Use b"abc\xff\xfe" for Python 3

    ###
    ### multiple statements
    ###

    cursor.execute("delete from foo; insert into foo values(1,2,3); create table bar(a,b,c) ; insert into foo values(4, 'five', 6.0)")

    ###
    ### iterator
    ###

    for x,y,z in cursor.execute("select x,y,z from foo"):
        print cursor.getdescription()  # shows column names and declared types
        print x,y,z

    ###
    ### iterator - multiple statements
    ###

    for m,n,o in cursor.execute("select x,y,z from foo ; select a,b,c from bar"):
        print m,n,o

    ###
    ### bindings - sequence
    ###

    cursor.execute("insert into foo values(?,?,?)", (7, 'eight', False))
    cursor.execute("insert into foo values(?,?,?1)", ('one', 'two'))  # nb sqlite does the numbers from 1

    ###
    ### bindings - dictionary
    ###

    cursor.execute("insert into foo values(:alpha, :beta, :gamma)", {'alpha': 1, 'beta': 2, 'gamma': 'three'})

    ###
    ### tracing execution
    ###

    def mytrace(cursor, statement, bindings):
        "Called just before executing each statement"
        print "SQL:",statement
        if bindings:
            print "Bindings:",bindings
        return True  # if you return False then execution is aborted

    cursor.setexectrace(mytrace)
    cursor.execute("drop table bar ; create table bar(x,y,z); select * from foo where x=?", (3,))

    | SQL: drop table bar ;
    | SQL: create table bar(x,y,z);
    | SQL: select * from foo where x=?
    | Bindings: (3,)

    ###
    ### tracing results
    ###

    def rowtrace(cursor, row):
        """Called with each row of results before they are handed off.  You can return None to
        cause the row to be skipped or a different set of values to return"""
        print "Row:", row
        return row

    cursor.setrowtrace(rowtrace)
    for row in cursor.execute("select x,y from foo where x>3"):
         pass

    | SQL: select x,y from foo where x>3
    | Row: (4, 'five')
    | Row: (7, 'eight')
    | Row: ('one', 'two')

    # Clear tracers
    cursor.setrowtrace(None)
    cursor.setexectrace(None)

    ###
    ### executemany
    ###

    # (This will work correctly with multiple statements, as well as statements that
    # return data.  The second argument can be anything that is iterable.)
    cursor.executemany("insert into foo (x) values(?)", ( [1], [2], [3] ) )

    # You can also use it for statements that return data
    for row in cursor.executemany("select * from foo where x=?", ( [1], [2], [3] ) ):
        print row

    ###
    ### defining your own functions
    ###

    def ilove7(*args):
        "a scalar function"
        print "ilove7 got",args,"but I love 7"
        return 7

    connection.createscalarfunction("seven", ilove7)

    for row in cursor.execute("select seven(x,y) from foo"):
        print row

    | ilove7 got (1, 2) but I love 7
    | (7,)
    | ilove7 got (4, 'five') but I love 7
    | (7,)
    | ilove7 got (7, 'eight') but I love 7
    | (7,)
    | ilove7 got ('one', 'two') but I love 7
    | (7,)
    | ilove7 got (1, 2) but I love 7
    | (7,)
    | ilove7 got (1, None) but I love 7
    | (7,)
    | ilove7 got (2, None) but I love 7
    | (7,)
    | ilove7 got (3, None) but I love 7
    | (7,)

    ###
    ### aggregate functions are more complex
    ###

    # Here we return the longest item when represented as a string.

    class longest:
        def __init__(self):
            self.longest=""

        def step(self, *args):
            for arg in args:
                if len( str(arg) ) > len (self.longest):
                    self.longest=str(arg)

        def final(self):
            return self.longest

        # Under Python 2.3 remove the following line and add
        # factory=classmethod(factory) at the end
        @classmethod
        def factory(cls):
            return cls(), cls.step, cls.final

    connection.createaggregatefunction("longest", longest.factory)
    for row in cursor.execute("select longest(x,y) from foo"):
        print row

    | ('eight',)

    ###
    ### Defining collations.
    ###

    # The default sorting mechanisms don't understand numbers at the end of strings
    # so here we define a collation that does

    cursor.execute("create table s(str)")
    cursor.executemany("insert into s values(?)",
                      ( ["file1"], ["file7"], ["file17"], ["file20"], ["file3"] ) )

    for row in cursor.execute("select * from s order by str"):
        print row

    | ('file1',)
    | ('file17',)
    | ('file20',)
    | ('file3',)
    | ('file7',)

    def strnumcollate(s1, s2):
        # return -1 if s1<s2, +1 if s1>s2 else 0

        # split values into two parts - the head and the numeric tail
        values=[s1, s2]
        for vn,v in enumerate(values):
            for i in range(len(v), 0, -1):
                if v[i-1] not in "01234567890":
                    break
            try:
                v=( v[:i], int(v[i:]) )
            except ValueError:
                v=( v[:i], None )
            values[vn]=v
        # compare
        if values[0]<values[1]:
            return -1
        if values[0]>values[1]:
            return 1
        return 0

    connection.createcollation("strnum", strnumcollate)

    for row in cursor.execute("select * from s order by str collate strnum"):
        print row

    | ('file1',)
    | ('file3',)
    | ('file7',)
    | ('file17',)
    | ('file20',)

    ###
    ### Authorizer (eg if you want to control what user supplied SQL can do)
    ###

    def authorizer(operation, paramone, paramtwo, databasename, triggerorview):
        """Called when each operation is prepared.  We can return SQLITE_OK, SQLITE_DENY or
        SQLITE_IGNORE"""
        # find the operation name
        print apsw.mapping_authorizer_function[operation],
        print paramone, paramtwo, databasename, triggerorview
        if operation==apsw.SQLITE_CREATE_TABLE and paramone.startswith("private"):
            return apsw.SQLITE_DENY  # not allowed to create tables whose names start with private

        return apsw.SQLITE_OK  # always allow

    connection.setauthorizer(authorizer)
    cursor.execute("insert into s values('foo')")
    cursor.execute("select str from s limit 1")

    | SQLITE_INSERT s None main None
    | SQLITE_SELECT None None None None
    | SQLITE_READ s str main None

    # Cancel authorizer
    connection.setauthorizer(None)

    ###
    ### progress handler (SQLite 3 experimental feature)
    ###

    # something to give us large numbers of random numbers
    import random
    def randomintegers(howmany):
        for i in xrange(howmany):
            yield (random.randint(0,9999999999),)

    # create a table with 100 random numbers
    cursor.execute("begin ; create table bigone(x)")
    cursor.executemany("insert into bigone values(?)", randomintegers(100))
    cursor.execute("commit")

    # display an ascii spinner
    _phcount=0
    _phspinner="|/-\\"
    def progresshandler():
        global _phcount
        sys.stdout.write(_phspinner[_phcount%len(_phspinner)]+chr(8)) # chr(8) is backspace
        sys.stdout.flush()
        _phcount+=1
        time.sleep(0.1) # deliberate delay so we can see the spinner (SQLite is too fast otherwise!)
        return 0  # returning non-zero aborts

    # register progresshandler every 20 instructions
    connection.setprogresshandler(progresshandler, 20)

    # see it in action - sorting 100 numbers to find the biggest takes a while
    print "spinny thing -> ",
    for i in cursor.execute("select max(x) from bigone"):
        print # newline
        print i # and the maximum number

    connection.setprogresshandler(None)

    ###
    ### commit hook (SQLite3 experimental feature)
    ###

    def mycommithook():
        print "in commit hook"
        hour=time.localtime()[3]
        if hour<8 or hour>17:
            print "no commits out of hours"
            return 1  # abort commits outside of 8am through 6pm
        print "commits okay at this time"
        return 0  # let commit go ahead

    connection.setcommithook(mycommithook)
    try:
        cursor.execute("begin; create table example(x,y,z); insert into example values (3,4,5) ; commit")
    except apsw.ConstraintError:
        print "commit was not allowed"

    connection.setcommithook(None)

    | in commit hook
    | no commits out of hours
    | commit was not allowed

    ###
    ### update hook
    ###

    def myupdatehook(type, databasename, tablename, rowid):
        print "Updated: %s database %s, table %s, row %d" % (
            apsw.mapping_authorizer_function[type], databasename, tablename, rowid)

    connection.setupdatehook(myupdatehook)
    cursor.execute("insert into s values(?)", ("file93",))
    cursor.execute("update s set str=? where str=?", ("file94", "file93"))
    cursor.execute("delete from s where str=?", ("file94",))
    connection.setupdatehook(None)

    | Updated: SQLITE_INSERT database main, table s, row 7
    | Updated: SQLITE_UPDATE database main, table s, row 7
    | Updated: SQLITE_DELETE database main, table s, row 7

    ###
    ### Blob I/O
    ###

    cursor.execute("create table blobby(x,y)")
    # Add a blob we will fill in later
    cursor.execute("insert into blobby values(1,zeroblob(10000))")
    # Or as a binding
    cursor.execute("insert into blobby values(2,?)", (apsw.zeroblob(20000),))
    # Open a blob for writing.  We need to know the rowid
    rowid=cursor.execute("select ROWID from blobby where x=1").next()[0]
    blob=connection.blobopen("main", "blobby", "y", rowid, 1) # 1 is for read/write
    blob.write("hello world")
    blob.seek(2000)
    blob.write("hello world, again")
    blob.close()

    ###
    ### Virtual tables
    ###

    # This virtual table stores information about files in a set of
    # directories so you can execute SQL queries

    def getfiledata(directories):
        columns=None
        data=[]
        counter=1
        for directory in directories:
            for f in os.listdir(directory):
                if not os.path.isfile(os.path.join(directory,f)):
                    continue
                counter+=1
                st=os.stat(os.path.join(directory,f))
                if columns is None:
                    columns=["rowid", "name", "directory"]+[x for x in dir(st) if x.startswith("st_")]
                data.append( [counter, f, directory] + [getattr(st,x) for x in columns[3:]] )
        return columns, data

    # This gets registered with the Connection
    class Source:
        def Create(self, db, modulename, dbname, tablename, *args):
            columns,data=getfiledata([eval(a.replace("\\", "\\\\")) for a in args]) # eval strips off layer of quotes
            schema="create table foo("+','.join(["'%s'" % (x,) for x in columns[1:]])+")"
            return schema,Table(columns,data)
        Connect=Create

    # Represents a table
    class Table:
        def __init__(self, columns, data):
            self.columns=columns
            self.data=data

        def BestIndex(self, *args):
            return None

        def Open(self):
            return Cursor(self)

        def Disconnect(self):
            pass

        Destroy=Disconnect

    # Represents a cursor
    class Cursor:
        def __init__(self, table):
            self.table=table

        def Filter(self, *args):
            self.pos=0

        def Eof(self):
            return self.pos>=len(self.table.data)

        def Rowid(self):
            return self.table.data[self.pos][0]

        def Column(self, col):
            return self.table.data[self.pos][1+col]

        def Next(self):
            self.pos+=1

        def Close(self):
            pass

    # Register the module as filesource
    connection.createmodule("filesource", Source())

    # Arguments to module - all directories in sys.path
    sysdirs=",".join(["'%s'" % (x,) for x in sys.path[1:] if len(x) and os.path.isdir(x)])
    cursor.execute("create virtual table sysfiles using filesource("+sysdirs+")")

    # Which 3 files are the biggest?
    for size,directory,file in cursor.execute("select st_size,directory,name from sysfiles order by st_size desc limit 3"):
        print size,file,directory

    | 24882176 testdb /space/apsw
    | 4045200 apsw.so /space/apsw
    | 915015 _yaml.so /home/rogerb/.local/lib/python2.7/site-packages

    # Which 3 files are the oldest?
    for ctime,directory,file in cursor.execute("select st_ctime,directory,name from sysfiles order by st_ctime limit 3"):
        print ctime,file,directory

    | 1388285092.49 setup.cfg /space/apsw
    | 1391490876.74 .gitignore /space/apsw
    | 1391584463.54 README.rst /space/apsw

    ###
    ### A VFS that "obfuscates" the database file contents.  The scheme
    ### used is to xor all bytes with 0xa5.  This scheme honours that used
    ### for MAPI and SQL Server.
    ###

    def encryptme(data):
        if not data: return data
        return "".join([chr(ord(x)^0xa5) for x in data])

    # Inheriting from a base of "" means the default vfs
    class ObfuscatedVFS(apsw.VFS):
        def __init__(self, vfsname="obfu", basevfs=""):
            self.vfsname=vfsname
            self.basevfs=basevfs
            apsw.VFS.__init__(self, self.vfsname, self.basevfs)

        # We want to return our own file implmentation, but also
        # want it to inherit
        def xOpen(self, name, flags):
            # We can look at uri parameters
            if isinstance(name, apsw.URIFilename):
                print "fast is", name.uri_parameter("fast")
                print "level is", name.uri_int("level", 3)
                print "warp is", name.uri_boolean("warp", False)
                print "notpresent is", name.uri_parameter("notpresent")

    | fast is speed
    | level is 7
    | warp is True
    | notpresent is None

            return ObfuscatedVFSFile(self.basevfs, name, flags)

    # The file implementation where we override xRead and xWrite to call our
    # encryption routine
    class ObfuscatedVFSFile(apsw.VFSFile):
        def __init__(self, inheritfromvfsname, filename, flags):
            apsw.VFSFile.__init__(self, inheritfromvfsname, filename, flags)

        def xRead(self, amount, offset):
            return encryptme(super(ObfuscatedVFSFile, self).xRead(amount, offset))

        def xWrite(self, data, offset):
            super(ObfuscatedVFSFile, self).xWrite(encryptme(data), offset)

    # To register the VFS we just instantiate it
    obfuvfs=ObfuscatedVFS()
    # Lets see what vfs are now available?
    print apsw.vfsnames()

    | ['unix', 'obfu', 'unix-excl', 'unix-dotfile', 'unix-none']

    # Make an obfuscated db, passing in some URI parameters
    obfudb=apsw.Connection("file:myobfudb?fast=speed&level=7&warp=on",
                           flags=apsw.SQLITE_OPEN_READWRITE | apsw.SQLITE_OPEN_CREATE | apsw.SQLITE_OPEN_URI,
                           vfs=obfuvfs.vfsname)
    # Check it works
    obfudb.cursor().execute("create table foo(x,y); insert into foo values(1,2)")

    # Check it really is obfuscated on disk
    print `open("myobfudb", "rb").read()[:20]`

    | '\xf6\xf4\xe9\xcc\xd1\xc0\x85\xc3\xca\xd7\xc8\xc4\xd1\x85\x96\xa5\xa1\xa5\xa4\xa4'

    # And unobfuscating it
    print `encryptme(open("myobfudb", "rb").read()[:20])`

    | 'SQLite format 3\x00\x04\x00\x01\x01'

    # Tidy up
    obfudb.close()
    os.remove("myobfudb")

    ###
    ### Limits
    ###

    # Print some limits
    for limit in ("LENGTH", "COLUMN", "ATTACHED"):
        name="SQLITE_LIMIT_"+limit
        maxname="SQLITE_MAX_"+limit  # compile time
        orig=connection.limit(getattr(apsw, name))
        print name, orig
        # To get the maximum, set to 0x7fffffff and then read value back
        connection.limit(getattr(apsw, name), 0x7fffffff)
        max=connection.limit(getattr(apsw, name))
        print maxname, max

    # Set limit for size of a string
    cursor.execute("create table testlimit(s)")
    cursor.execute("insert into testlimit values(?)", ( "x"*1024, )) # 1024 char string
    connection.limit(apsw.SQLITE_LIMIT_LENGTH, 1023) # limit is now 1023
    try:
        cursor.execute("insert into testlimit values(?)", ( "y"*1024, ))
        print "string exceeding limit was inserted"
    except apsw.TooBigError:
        print "Caught toobig exception"
    connection.limit(apsw.SQLITE_LIMIT_LENGTH, 0x7fffffff)

    | SQLITE_LIMIT_LENGTH 1000000000
    | SQLITE_MAX_LENGTH 1000000000
    | SQLITE_LIMIT_COLUMN 2000
    | SQLITE_MAX_COLUMN 2000
    | SQLITE_LIMIT_ATTACHED 10
    | SQLITE_MAX_ATTACHED 10
    | Caught toobig exception

    ###
    ### Backup to memory
    ###

    # We will copy the disk database into a memory database

    memcon=apsw.Connection(":memory:")

    # Copy into memory
    with memcon.backup("main", connection, "main") as backup:
        backup.step() # copy whole database in one go

    # There will be no disk accesses for this query
    for row in memcon.cursor().execute("select * from s"):
        pass

    ###
    ### Shell
    ###

    # Here we use the shell to do a csv export providing the existing db
    # connection

    # Export to a StringIO
    import StringIO as io # use io in Python 3
    output=io.StringIO()
    shell=apsw.Shell(stdout=output, db=connection)
    # How to execute a dot command
    shell.process_command(".mode csv")
    shell.process_command(".headers on")
    # How to execute SQL
    shell.process_sql("create table csvtest(col1,col2); insert into csvtest values(3,4); insert into csvtest values('a b', NULL)")
    # Let the shell figure out SQL vs dot command
    shell.process_complete_line("select * from csvtest")

    # Verify output
    print output.getvalue()

    | col1,col2
    | 3,4
    | a b,
    |

    ###
    ### Statistics
    ###

    print "SQLite memory usage current %d max %d" % apsw.status(apsw.SQLITE_STATUS_MEMORY_USED)

    | SQLite memory usage current 420072 max 494080

    ###
    ### Cleanup
    ###

    # We can close connections manually (useful if you want to catch exceptions)
    # but you don't have to
    connection.close(True)  # force it since we want to exit

    # Delete database - we don't need it any more
    os.remove("dbfile")

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