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### Non-VM instructions (e.g. Macs)
- Create db w/ `createdb flightsskewed`.
-- Ensure that the *user* in SQLTesting.py matches your user account.
## Submission
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+## Project 3: Object-Relational Mappings
+
+*The assignment is to be done by yourself.*
+
+Two parts: `psycopg` and `peewee`.
+
+### Setup
+
+Download the startup files [here](https://ceres.cs.umd.edu/424/assign/assignment3Dist.tgz?2).
+
+As before, use the Dockerfile to create and start an image: build (`docker build --rm -t 424 .`) and run (`docker run -it -v $(pwd):/424 424`) .
+Ensure that the database that
+the `flightsskewed` database exists, and that tables are populated from `large-skewed.sql`. Use
+`flightsskewed` for all parts of this assignment.
+
+## Your Tasks
+
+**Task 1: External clients (25 pts)**: One of more prominent ways to use a database system is using an
+external client, using APIs such as ODBC and JDBC, or the
+Python DB-API 2.0 specification.
+
+We will be using the [psycopg](http://initd.org/psycopg/) instantiation of the Python DB spec to access the
+database. There are many good tutorials, such as this
+[Postgres/psycopg Tutorial](http://www.postgresqltutorial.com/postgresql-python),
+the [default documentation](http://initd.org/psycopg/docs/usage.html#passing-parameters-to-sql-queries) is quite good,
+and you can also
+get see a working example of queries in *SQLTesting.py* from Project 1.
+
+For those new to Python, I recommend the
+[Python Tutorial](https://docs.python.org/3/tutorial/index.html).
+
+Your task to write a single Python function `runPsy()` function, in
+file `psy.py`, that reads in a JSON file and updates the database
+appropriately. `runPsy()` should take three parameters:
+- `conn`: the database connection, already opened and initialized
+- `curs`: a *cursor* for the connection.
+- `jsonFile`: the JSON file name
+
+Database cursors implement the notion of a *session* with respect to a single
+connection. Cursors are used to execute commands and return results, whether
+one by one or all at once.
+
+Each line in the input file will consist of a single JSON object in one of the following two formats:
+
+- **New customer**, where information about a customer is provided in the following format
+ (though our example file has each input in a single line). You can assume that the
+ frequent flier airline name matches exactly what is there in the 'airlines' table.
+
+```
+{ "newcustomer": {
+ "customerid": "cust1000",
+ "name": "XYZ",
+ "birthdate": "1991-12-06",
+ "frequentflieron": "Spirit Airlines"
+ }
+}
+```
+
+- **Flew On**, where information about the passengers in a flight is
+provided. Create new rows in `flewon` for each customer, as well as the `customers`
+table if the `customerid` does not already exist.
+ - In some cases the `customerid` provided may not be present in the database (cust1000 as seen below). In this case, first update the `customers` table (all the info is guaranteed to be
+there), and then add tuples to the `flewon` table.
+
+```
+{ "flewon": {
+ "flightid": "DL108",
+ "flightdate": "2015-09-25",
+ "customers": [
+ {"customerid": "cust1001", "name": "XYZ", "birthdate": "1991-12-06", "frequentflieron": "AA"},
+ {"customerid": "cust25"}, {"customerid": "cust33"}
+ ]
+ }
+}
+```
+
+### Testing
+
+`python3 testPsy.py`
+
+Notes:
+
+1. In the case of either of the following errors, you should just print "Error424" and then exit. You do not need to handle any other errors.
+ - If the `customerid` for a `newcustomer` update is already present, or
+ - if the `frequentflieron` does not have a match in the airlines table
+2. Be sure to *commit()* the database connection at the end. Otherwise, no data will be modified.
+3. `example.json` is an example input file consisting of the JSON input
+ above. We will test on a slightly different input file.
+4. There are many Python JSON parsing libraries, but the simplest to use is the
+[json module](https://docs.python.org/3/library/json.html) from the
+[Python standard library](https://docs.python.org/3/library/).
+5. `./clean-example.py` will remove the tuples added from `example.py`.
+
+
+## Task 2: Object-Relational Mappings (`peewee`) (35 pts)
+
+Another way to use a database is through an object-relational-mapping (ORM),
+which maps table rows onto objects that are visible in a programming
+language. The result is that you can write a database application without
+using SQL at all.
+
+We will re-write the previous program with exactly the same semantics, but using an object
+model approach instead. There are many Python ORMs, including Django, but we
+will use the simpler [Peewee](http://docs.peewee-orm.com/en/latest/peewee/quickstart.html#quickstart).
+
+Your goal will to create a function `runOrm()`, parameterized by JSON
+file name, and implements the same functionality as above.
+
+Create your file by using a Peewee distribution tool called `pwiz`, which uses database
+ *introspection* to create python classes mirroring an existing postgres schema. Use as follows:
+```
+ pwiz.py -e postgresql -u root -P flightsskewed > orm.py # password is `root`
+```
+This will create the scaffolding of your ORM program in `orm.py`.
+
+
+Test this code as follows:
+- Add `from datetime import date` to the top of `orm.py`.
+- Add the following lines to the end of the file:
+```
+def runORM(jsonFile):
+ Customers.delete().where(Customers.name == 'bob').execute()
+ Airports.delete().where(Airports.airportid == 'PET').execute()
+
+ bob = Customers(name="bob", customerid='cust1010', birthdate='1960-01-15', frequentflieron='SW')
+ bob.save(force_insert=True)
+
+ bwi = Airports(airportid='PET', city='Takoma', name='Pete', total2011=2, total2012=4)
+ bwi.save(force_insert=True)
+
+ for port in Airports.select().order_by(Airports.name):
+ print (port.name)
+```
+
+Run by typing `python3 testORM.py` from the shell. You should have a record added to each of
+*customers* and *airports*, followed by a listing of all airport
+names. Verify that `bob` and `PET` were added using `psql`.
+
+### SubTask 1: Replicate the work in `psy.py` (25 pts)
+Remove all the lines of `runORM()`. Replace them with code to
+implement the same changes to
+the database as in `psy.py` (read JSON strings, insert corresponding tuples into the
+database), but do so entirely through the **Peewee** ORM interface.
+
+### SubTask 2: Update `NumberOfFlightsTaken` (10 pts)
+Add code in `runORM` to update `NumberOfFlightsTaken` as in assign2, which has
+already been defined (but not populated). In other words, clear out the table and repopulate it from scratch each time runORM() is called.
+
+
+
+## Notes
+- You must add `.save(force_insert=True)` for new tuples or they will not be committed to the
+ database.
+- `python3 SQLTesting.py` is once again your last step. Run this and it will call both
+ of your functions. Getting this to work means that your code will probably
+ also work on Gradescope.
+- You might or might not need to eliminate blank lines before " class Meta:" lines in
+ order to avoid syntax errors, i.e. get rid of any blank lines
+ within class definitions (or ensure that proper indentation is maintained by adding spaces).
+
+
+## Native mac / non-docker installations
+On an apple-silicon mac you must:
+- ensure python3/pip3 are installed
+- `sudo pip3 install psycopg2`
+- `sudo pip3 install peewee`
+- ensure that the DB connections in the `test*.py` files are using a local name rather than vagrant, i.e.:
+```
+conn = psycopg2.connect("dbname=flightsskewed user=keleher")
+```
+instead of:
+```
+conn = psycopg2.connect("dbname=flightsskewed user=vagrant password=vagrant")
+```
+Password for the local name should be the empty password. However, note that you still have to use the root version when submitting to gradescope!
+
+Also, be sure you have:
+```
+ database = PostgresqlDatabase('flightsskewed', **{'host': 'localhost', 'user': 'root', 'password': 'root'})
+```
+in `orm.py`.
+
+## Submit Instructions
+Submit `psy.py` and `orm.py` files by compressing (zip: on a mac
+select them both and right-click "select") them to an archive with two
+files, and then dropping that archive on to the <a href="https://www.gradescope.com/courses/811728/assignments/4669997">Assignment 3 submission</a>.