Understanding JSON and Data Access Objects

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Questions and Answers

What is a key advantage of using plain text for storage?

More secure than binary formats

No need for manual editing

Human readable (correct)

Takes up less memory

Which of the following correctly describes a JSON object?

A single name with multiple values

A string formatted in JSON

An ordered list of name-value pairs

An unordered set of name-value pairs (correct)

In JSON, what must follow each name in a name/value pair?

A colon (correct)

A comma

A semicolon

A period

What data types can values in JSON be?

Strings, numbers, objects, arrays, booleans, and null Signup and view all the answers

Which statement correctly describes how strings must be formatted in JSON?

Strings must be in double quotes only Signup and view all the answers

How are name/value pairs separated in a JSON object?

By commas Signup and view all the answers

Which of the following is a valid format for an array in JSON?

[ 'John', 'Anna', 'Peter' ] Signup and view all the answers

What is the primary purpose of using JSON?

To provide a human-readable data interchange format Signup and view all the answers

What is the purpose of the UserDAO class?

To define the methods required for user data access. Signup and view all the answers

Which method in the UserDAOSQLite class retrieves a user based on their ID?

get_user_by_id Signup and view all the answers

What is a key feature of the User class?

It encapsulates the user data attributes. Signup and view all the answers

In the UserDAOSQLite class, what does the insert_user method do?

Inserts a new user into the users table. Signup and view all the answers

What does the commit method do in the context of the DAO implementation?

Saves changes made during the current transaction. Signup and view all the answers

Which SQL command is used to update a user's information?

UPDATE Signup and view all the answers

What does the get_all_users method return?

A list of all users in the database. Signup and view all the answers

In the main function, which operation is performed first after creating a UserDAOSQLite instance?

Inserting a new user. Signup and view all the answers

What is the purpose of the Student model class?

To represent individual students with their details. Signup and view all the answers

Which method in the School class is responsible for returning a list of all students?

list_all() Signup and view all the answers

What should the StudentDAO interface methods return when a new student is successfully created?

A boolean indicating success Signup and view all the answers

In the context of persistence, what constitutes a simple solution?

Loading the students’ file into the student collection within the School constructor. Signup and view all the answers

Which of the following is NOT a method defined in the StudentDAO interface?

count_students() Signup and view all the answers

What component of the Student class allows for comparing two Student objects?

eq() Signup and view all the answers

What is the primary role of the School class in the model?

To serve as a storage container for multiple students. Signup and view all the answers

Which statement about the age() method in the Student class is true?

It calculates the age based on the current year. Signup and view all the answers

What is a disadvantage of saving the full student collection into the students' file after each operation?

It limits the ability to change persistence technologies. Signup and view all the answers

Why is using a DAO structure considered a better solution?

It centralizes data access methods. Signup and view all the answers

What is the role of the 'autosave' parameter in testing?

To control whether collections or persistence are tested together. Signup and view all the answers

What happens when autosave is turned off by default?

Only collection functionality is tested. Signup and view all the answers

How is the ConcreteStudentDAO expected to be chosen?

It should be replaced based on the chosen persistence technology. Signup and view all the answers

In the class refactoring, what parameter is passed to the ConcreteStudentDAO?

The autosave setting. Signup and view all the answers

What approach is taken to manage testing between collection and persistence functionalities?

System properties are used to separate testing. Signup and view all the answers

If using a database or cloud storage, what is the testing focus?

Only the persistence aspect. Signup and view all the answers

What is the correct method to read an object from a file using the pickle module?

load(fileobj) Signup and view all the answers

Which of the following objects can be pickled?

Any object type Signup and view all the answers

What will an EOFError indicate while loading data from a pickle file?

The end of the file has been reached Signup and view all the answers

What is one way to save a list of objects using pickle?

Using the dump method in a loop Signup and view all the answers

In the example of saving a list of objects, which attribute is NOT part of the Student class?

age Signup and view all the answers

How can elements be saved one at a time in a list using the pickle module?

Using dump within a loop for each element Signup and view all the answers

What happens to the data when using the 'with' statement while opening files?

It closes the file automatically after operations Signup and view all the answers

What is the primary purpose of pickling in Python?

To serialize and deserialize Python objects Signup and view all the answers

When loading a list with an unknown size, what should be done to handle reaching the end of the file?

Handle EOFError exception Signup and view all the answers

What does the `dump` function do in the context of the pickle module?

Writes an object to a file Signup and view all the answers

In the example given, which input type is used to collect grades for students?

Floating-point number Signup and view all the answers

What will be printed when a list is successfully retrieved after being pickled and unpickled?

The list in a human-readable format Signup and view all the answers

What format does the pickle module use to store object data?

Binary format Signup and view all the answers

Which of the following is NOT a valid way to open a file for writing using the pickle module?

open('file.dat', 'w') Signup and view all the answers

What is the first step in setting up a unit test for the School class?

Start with no files or an empty database Signup and view all the answers

What method is called to reset the persistence mechanism after each CRUD operation?

reset_persistence Signup and view all the answers

In the test_create_search method, what is expected when creating a new student?

It should return true on success Signup and view all the answers

How does the tearDown method ensure data integrity between tests?

By removing any created files after each test Signup and view all the answers

What is indicated when the test_update method returns false for an unregistered student?

The student could not be found in the records Signup and view all the answers

Which assertion checks if a student was successfully deleted from the school records?

assertTrue with a deleted student ID Signup and view all the answers

What do the tests conducted in the SchoolTest class primarily help verify?

The integrity of student data management operations Signup and view all the answers

In the test_list_all method, what should the length of the student list be after deleting all students?

0 Signup and view all the answers

How is a singleton list verified in the retrieve method?

By asserting that the length equals 1 and matches the correct student Signup and view all the answers

What does the School class's create method return upon a successful addition of a student?

A boolean value of true Signup and view all the answers

What happens if a user tries to delete a student who has already been removed?

It returns false as the deletion cannot occur Signup and view all the answers

What is the expected outcome when calling the update method with the correct student ID?

The method should return true if successful Signup and view all the answers

Which of the following is a reason to implement strict persistence testing according to the SchoolTest?

To prevent multiple test cases from interacting Signup and view all the answers

Study Notes

Persistence with Files in Python

Python uses the open() function to work with files.
This function accepts a file name and a mode as arguments.
The mode determines how the file will be opened (e.g., 'r' for reading, 'w' for writing, 'a' for appending).

Files in Text Mode

Text files store information as characters.
Writing to a text file:
- Open the file in write mode ('w').
- Use the write() method to add text (must be a string).
- Close the file when finished, to ensure data is written.
Copying a file:
- Open an existing file to read ('r').
- Open another file to write ('w').
- Read the content from the first file.
- Write the content to the second file.
- Close both files.
Copying a list of numbers into a file:
- Define an empty list.
- Take input for list size.
- Get list elements as input.
- Append elements to the list.
- Open the file in write mode.
- Write the list size.
- Write each list element in the file, on a new line.
- Close the file.

Text file commands in Python

File objects represent files in Python.
open() opens a file, specifying the file path and mode.
Modes: 'r' - read, 'w' - write, 'a' - append, 'r+' - read and write (start of file), 'w+' - create and write or read.

File commands in Python

fileobj.write(str): Writes a string to the file.
fileobj.read(): Reads the entire file content as a string.
fileobj.readline(): Reads one line from the file.
fileobj.close(): Closes the file.

The with command

The with statement simplifies file handling:
- Automatically closes the file, even if errors occur.

Example using the with command

Creating and writing a list of numbers into a file.
Reading a list of numbers from a file.

Files in Binary Mode

Binary files store information as bytes.
Opening in binary mode: Use 'b' as part of the mode (e.g., 'rb', 'wb').
Modes: rb: read-only binary, wb: write-only binary, ab: read and write (append to end binary), r+b: read/write binary at start of file, w+b: reads/write, always creates new file, if it does not exist.
Example file = open('data.dat', 'wb')

Pickle Library

The pickle library serializes and deserializes complex Python objects to files.
Serializing: Stores Python objects (e.g., lists, dictionaries) in a file.
Deserializing: Reads objects from a file.
pickle.dump(object, fileobj) writes objects into a file, while pickle.load(fileobj) reads objects from a file.
Use the with statement with wb or rb for binary mode.

JSON

JSON (JavaScript Object Notation) is a text interchange format.
It's human-readable and easily parsable by other programming languages.
Data types supported in JSON: numbers, strings, booleans, objects, and arrays.
Use the Python json module to work with JSON.
Example: { "name": "John Doe", "age": 30, "city": "New York"

}

JSON Basics in Python

Python's json module helps use JSON in Python.
json.load() reads a JSON file and converts it to a Python object.
json.dumps() converts a Python object to a JSON string.

DAO Pattern

Data Access Object (DAO) pattern decouples business logic from database operations.
The goal of the pattern is to ensure that data source does not affect application logic, and can be changed as needed.
Create an interface (UserDAO): defines the methods for managing data.
Create an implementation (UserDAOSQLite) which defines how to perform CRUD operations.

DAO Behavior

Shows the interaction between the client, UserDAO and the database.
Illustrates how the DAO pattern is used to encapsulate data source access.

DAO Structure

A visual representation of the DAO pattern's components (interface, implementation, model object, and client). Shows the dependency relationships between the classes.

Persistence Testing

A testing method to enforce data consistency between application and database.
Use setUp() and tearDown to manage testing environment between each test method.
reset method to ensure files are cleared before each test run.

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Description

This quiz assesses your knowledge of JSON structure, usage, and its integration with Data Access Objects (DAO). Explore concepts like JSON format, data types, and methods within DAO classes like UserDAO. Test your understanding of these key technology components with this comprehensive quiz.