Programming Fundamentals course. Mathematics and Computer Science Faculty at SPbU

Project #2: Key-Value Database

Task (in Russian)

Usage

distribution/bin/pf-2021-kvdb [OPTIONS] [DATABASETOOPEN] (run from root directory)

Console utility kvdb provides command-line interface to work with simple key-value database (which internally is JSON).

Interface

Once launched, you get into interactive shell. Enter your command and press Enter to evaluate it. Enter ...> help to get the list of commands with explanations.

Input

To open a database, you either have to provide DATABASETOOPEN argument like this: java -jar kvdb db.json, or enter ...> open db.json while in the interactive shell. If database was loaded successfully, the input prompt will change to db.json> .

Input from file

If you have a script (sequence of commands) to edit some database, use java -jar kvdb -q < script.txt. In this case you'll find OPTION -q or --quiet useful. This option suppresses input prompt ...> , which is printed incorrectly if commands are read from file.

Output

The format of output is human-readable. Further details are provided in the Commands overview section.

Commands overview

Command	Explanation
open [ARG1]	Open database from file located at [ARG1]. Error messages: <FILE> does not exist., <FILE> is not a normal file., <FILE> is not readable., <FILE> contains malformed data.
new [ARG1]	Create empty database at [ARG1]. Error messages: Couldn't create file.
store [ARG1] [ARG2]	Assign value [ARG2] to [ARG1] key (if either argument contains spaces, use ""). Note that if key [ARG1] is present in the database, the previous value is overwritten.
get [ARG1]	Get value assigned to [ARG1] key (if key contains spaces, use ""). Error messages: There is no <KEY> key in the database..
list	Print all the key value pairs in the database. Format of output: each pair is printed on separate line in following format:"<KEY>": "<VALUE>".
delete [ARG1]	Get value assigned to [ARG1] key (if key contains spaces, use ""). Error messages: There is no <KEY> key in the database..
save	Save database to the file (by overwriting it).
move [ARG1]	Change the destination of saving to [ARG1]. If file exists at path [ARG1], save will overwrite it. Otherwise, a new file will be created.
close	Save and close database.
help	Print list of all available commands with explanations.
quit	Save the database (if opened) and quit the program.

Getting help

Use -h or --help option to get information about OPTIONS and DATABASETOOPEN. Use ...> help inside interactive shell to show list of available commands.

Testing

All files related to external testing are now in an ext_tests directory. Run ext_tests/test.sh script.txt to run a simple script (saved in ext_tests/script.txt) that contains few operations with database. There is also ext_tests/big_script.txt, that contains 1000 operations with database:

1. create a new database,
2. insert a key and value,
3. close database,
4. reopen it,
5. repeat from 2

This script is generated with ext_tests/gen_big_script.sh 1000. Use ext_tests/test.sh big_script.txt to run it and see the time of execution.