PCPP2 Database Access — 20 Questions

Question 1

In a PyMongo application, what happens when you use 'insert_many' with 'ordered=False'?

Accepted Answer

The driver attempts to insert all documents regardless of individual failures.. If 'ordered' is False, the driver continues to insert subsequent documents even if one fails.

Answer

The driver ignores all errors.

Answer

Documents are inserted in parallel.

Answer

The operation stops at the first error.

Question 2

When using SQLAlchemy Declarative Base, how do you define a table name that differs from the class name?

Accepted Answer

Set __tablename__ = 'name'. The __tablename__ attribute is used to explicitly map a class to a specific table name.

Answer

Set __table_name__ = 'name'

Answer

Map it in the metadata object.

Answer

Use the 'table' argument in the class definition.

Question 3

In SQLAlchemy, what is the difference between 'lazy='select'' and 'lazy='joined'' loading strategies?

Accepted Answer

select loading executes a separate SQL statement when the attribute is first accessed.. joined loading performs an outer join to fetch related objects in the same query, whereas select loading fetches them only when accessed.

Answer

joined loading causes N+1 query problems.

Answer

joined loading is always faster.

Answer

select loading is the default for all relationships.

Question 4

You are using SQLAlchemy with an asynchronous driver (asyncio). Which object must be used to perform database operations asynchronously?

Accepted Answer

AsyncSession. AsyncSession is the required class for asynchronous session management in SQLAlchemy.

Answer

Engine.async

Answer

None of the above

Answer

AsyncConnection

Answer

Session

Question 5

You are developing an application using SQLAlchemy and need to retrieve a single object by its primary key. Which method is preferred for this operation?

Accepted Answer

session.get(Model, pk). The get() method on the Session object is the optimized way to retrieve an object by its primary key.

Answer

Model.find(pk)

Answer

session.fetch(Model, pk)

Answer

session.query(Model).filter(Model.id == pk).first()

Question 6

You are using sqlite3 in Python and need to ensure that data integrity is maintained when performing multiple related INSERT operations. Which method should you call on the connection object to commit your changes?

Accepted Answer

connection.commit(). The commit() method is used to save the current transaction to the database.

Answer

connection.save()

Answer

connection.flush()

Answer

cursor.apply()

Question 7

When using the sqlite3 module, what is the primary purpose of using a context manager (the 'with' statement) on a connection object?

Accepted Answer

To automatically commit or rollback transactions.. In sqlite3, the connection context manager automatically commits or rolls back transactions.

Answer

To lock the database file for exclusive access.

Answer

To automatically close the connection upon exit.

Answer

To parse SQL queries for syntax errors.

Question 8

When connecting to a MongoDB instance using PyMongo, what is the role of the 'MongoClient' object?

Accepted Answer

It serves as the main connection handle to the MongoDB cluster.. The MongoClient acts as the entry point to the MongoDB server, allowing access to databases and collections.

Answer

It stores individual documents in memory.

Answer

It defines the schema for BSON documents.

Answer

It translates SQL queries into MQL.

Question 9

Which of the following best describes the benefit of using parameterized queries in sqlite3?

Accepted Answer

They prevent SQL injection attacks.. Parameterized queries prevent SQL injection by separating the query logic from the data.

Answer

They allow for multiple database connections.

Answer

They improve query execution speed by pre-compiling.

Answer

They automatically format the output as JSON.

Question 10

In SQLAlchemy, what does the 'metadata.create_all(engine)' command do?

Accepted Answer

It creates tables for all models bound to the metadata.. It inspects the defined ORM models and emits CREATE TABLE statements to the database.

Answer

It connects to the database and tests the latency.

Answer

It drops all tables and recreates them.

Answer

It populates the tables with initial data.

Question 11

In sqlite3, how do you handle a database error such as a constraint violation?

Accepted Answer

Use a try-except block to catch sqlite3.Error.. You should wrap database operations in a try-except block and catch sqlite3.Error or its subclasses.

Answer

Check the connection status after every query.

Answer

Check the return value of the execute() method.

Answer

The library crashes the program automatically.

Question 12

When performing bulk inserts in PyMongo, which method is the most efficient?

Accepted Answer

insert_many. insert_many is designed to send multiple documents in a single batch to the server.

Answer

save

Answer

Looping insert_one

Answer

bulk_write

Question 13

Which PyMongo method should be used to update a single document if you want to modify specific fields without replacing the entire document?

Accepted Answer

update_one. The update_one method with the $set operator allows updating specific fields.

Answer

upsert

Answer

save

Answer

replace_one

Answer

update_many

Question 14

Which object in SQLAlchemy is responsible for maintaining a collection of loaded objects and managing their lifecycle?

Accepted Answer

Session. The Session object acts as a workspace for objects and tracks their state.

Answer

Engine

Answer

Query

Answer

MetaData

Question 15

When using the MongoDB aggregation framework in PyMongo, which stage should be used to filter documents based on a condition?

Accepted Answer

$match. The $match stage is used to filter documents in an aggregation pipeline.

Answer

$group

Answer

$project

Answer

$filter

Question 16

You are using SQLAlchemy's relationship() function. What does 'back_populates' achieve?

Accepted Answer

It synchronizes the two sides of the relationship in Python memory.. It links two sides of a relationship so that changes in one are reflected in the other via the session's identity map.

Answer

It improves query performance.

Answer

It automatically cascades deletes.

Answer

It forces a database level foreign key constraint.

Question 17

Which Python library is the standard built-in interface for SQLite databases?

Accepted Answer

sqlite3. The 'sqlite3' module is part of the Python standard library.

Answer

pymongo

Answer

sqlalchemy

Answer

db-api

Question 18

Which command-line tool is typically used to inspect the contents of a SQLite database file?

Accepted Answer

sqlite3. The 'sqlite3' command-line interface is the standard tool to interact with .db files.

Answer

mysql

Answer

mongo

Answer

psql

Question 19

What is the purpose of the 'upsert=True' option in MongoDB update operations?

Accepted Answer

It creates a new document if no match is found.. If no document matches the query, a new document is created with the update criteria.

Answer

It prevents duplicates.

Answer

It sorts the results before updating.

Answer

It forces an atomic update across a cluster.

Question 20

When configuring a connection pool in SQLAlchemy, what does the 'pool_size' parameter define?

Accepted Answer

Number of persistent connections kept in the pool.. pool_size defines the number of persistent connections to keep open in the pool.

Answer

The number of retries before failure.

Answer

The timeout duration for queries.

Answer

Maximum number of simultaneous sessions.