Day 27

Day 22-24 (architecture)/SystemArchitecture.md

@@ -17,7 +17,7 @@ For a database engine, SQLite was compared with MySQL, as both are free.  Accord
 
 #### Backups
 
-SQLite works based on a single database file, so it will be straightforward to schedule automatic backups.  For simplicity of deployment, the plan is to implement this in the Node.js server script itself.
+SQLite works based on a single database file and it has built-in functionality for making a backup, so it will be straightforward to schedule automatic backups.  For simplicity of deployment, the plan is to implement this in the Node.js server script itself.
 
 ### Client-server data communication: JSON over AJAX
 
@@ -29,6 +29,8 @@ JSON will be used for client-server data communication (e.g. visit and user data
 
 ## Major database tables
 
+There will only need to be 3 main database tables: Users, Visits, and Committments.  These tables will implement the internal model supposed in the user interface document.  There will also be a table for storing configuration data; see https://stackoverflow.com/questions/2300356/using-a-single-row-configuration-table-in-sql-server-database-bad-idea for a discussion of two possible implementations of the configuration table.
+
 ## Performance
 
 ## Scalability

Day 24-27 (database)/Database selection.txt

@@ -0,0 +1,49 @@
+DBMS = Database Management System (e.g. MySQL, MariaDB, PostgreSQL, Oracle, Access, MongoDB)
+
+SQL:
+	This should be your default option for most applications
+	Relational database with predefined schema
+	Data organized in tables, rows, and columns
+	Uses SQL as a common language, but some features may be DBMS-specific (MySQL vs PostgreSQL, etc.)
+	Well-suited for multi-table transactions
+
+NoSQL:
+	Useful when you need high-performance at a huge scale, with little or no relation between tables
+	Allows storing data with no schema
+	Well-suited for documents, JSON, time series data, data dumps, and logs
+	Records can have internal structure (such as an array or tree-like structure)
+	Lack of good support for joins can be circumvented by storing joined data multiple times in different records 
+		This sacrifices memory for time
+		Maintaining data consistency is more challenging
+	Some NoSQL DMBSs have limited support for joins and transactions
+
+Note: If you just need to dump a bunch of JSON data (or something similar) from your application and fetch it back at a later time, you may not need a detailed database model.  You may just want to store the JSON data directly (which both SQL and NoSQL databases can do).
+
+SQLite:
+	From their website: "SQLite does not compete with client/server databases.  SQLite competes with fopen()"
+	Benefits:
+		Simple to setup
+		Low latency, even for large sequences of SQL statements
+		Transactional
+		Serverless
+		Single data file
+		Lightweight processing
+	Drawbacks:
+		Any write operation requires a lock on the whole database; many simultaneous writes will slow it down
+		Lacks stored procedures
+		Lacks user management (e.g. who has permission to write to which table)
+
+Transaction:
+	A unit of work on the database (possibly with multiple actions), treated independently of other such units.
+	If you are using a database, you must learn how to use transactions
+	Properties (ACID):
+		Atomic - either all of the transaction takes affect, or none of it (including under power failures and crashes)
+		Consistent - database invariants are maintained (constraints, triggers, referential integrity, etc.)
+		Isolated - transactions are executed as if they were sequential
+		Durable - committed transactions are never forgotten (i.e. they stored to non-volatile memory)
+
+Basic operations (CRUD) and their associated SQL statements:
+	Create (INSERT)
+	Retrieve (SELECT)
+	Update (UPDATE)
+	Delete (DELETE)

Day 24-27 (database)/notes.txt

@@ -0,0 +1,107 @@
+Naming conventions I'll be using:
+	UpperCamelCase tables and columns
+	Plural table names (less likely to conflict with reserved words)
+	Singular column names
+	Associative table names:
+		The names the other two tables joined by an underscore: either can be singular or plural as the relationship dictates.
+	Primary keys are named [SingularTableName]ID, and identically when appearing as a foreign key.
+		When needed, add a prefix: SourceWarehouseID and DestinationWarehouseID
+
+Some SQLite specific commands
+	.open CampusVisit.db
+	.tables
+	PRAGMA table_info(TableName);
+	PRAGMA foreign_keys = ON;  /* Need this one to define foreign key contraints. */
+
+CREATE TABLE Users(
+	UserID INTEGER PRIMARY KEY,
+	Name VARCHAR(100) UNIQUE NOT NULL,
+	Email VARCHAR(20) UNIQUE NOT NULL,
+	PasswordHash VARCHAR(64) NOT NULL,
+	IsAdmin BOOLEAN NOT NULL,
+	IsFaculty BOOLEAN NOT NULL,
+	IsCoordinator BOOLEAN NOT NULL,
+	Availability INTEGER DEFAULT -9223372036854775808  /* 64 bits.  LSB is Sunday 8am, then 9am, 10, ... Monday 8am, 9am, ....  Sign bit is "other time" category. */
+);
+
+CREATE TABLE Visits(
+	VisitID INTEGER PRIMARY KEY,
+	UserID INTEGER,  /* DEFAULT NULL is implicit in SQLite.  NULL values are allowed with the foreign key. */
+	StudentInfo VARCHAR(100) NOT NULL DEFAULT '',
+	OtherVisitors VARCHAR(100) NOT NULL DEFAULT '',
+	Hometown VARCHAR(50) NOT NULL DEFAULT '',
+	Day VARCHAR(10) NOT NULL,  /* YYYY-MM-DD */
+	Availability INTEGER NOT NULL DEFAULT 0,   /* Same format as Users.Availability */
+	DecidedTime INTEGER,   /* Same format as Users.Availability */
+	Status VARCHAR(9) CHECK(Status IN ('proposed','assigned','confirmed','completed','canceled')) NOT NULL DEFAULT 'proposed',
+	Notes VARCHAR(500) NOT NULL DEFAULT '',
+	NotificationFrequency INTEGER NOT NULL DEFAULT 2,
+	FOREIGN KEY(UserID) REFERENCES Users(UserID)
+);
+
+CREATE TABLE Visits_Users (
+	VisitID INTEGER,
+	UserID INTEGER,
+	Willingness VARCHAR(10) CHECK(Willingness IN ('cannot', 'prefer not', 'can do')) NOT NULL, /* unknown if pair is missing from the table */
+	PRIMARY KEY (VisitID, UserID),
+	FOREIGN KEY(VisitID) REFERENCES Visits(VisitID),
+	FOREIGN KEY(UserID) REFERENCES Users(UserID)
+);
+
+CREATE TABLE Settings(
+	 Key VARCHAR(100) PRIMARY KEY,
+	 Value VARCHAR(100) NOT NULL DEFAULT ''
+);
+
+Initialization:
+	Initial values for global settings (hyperlink lifetime and notification frequency)
+		INSERT INTO Settings VALUES ('HyperlinkLifetime','7');
+		INSERT INTO Settings VALUES ('CoordinatorNotificationFrequency','3');
+Login screen:
+	Check username/password
+		SELECT COUNT() FROM Users WHERE Email='mkowalcz@nmu.edu' AND PasswordHash='secret';
+Visits tab:
+	Create new visit
+		INSERT INTO Visits (StudentInfo,Day) VALUES ('Joe Bloggs, Major: CS', '2025-04-15');
+	Get list of all visits, joined with faculty guides
+		SELECT Visits.VisitID,Visits.StudentInfo,Users.name FROM Visits LEFT JOIN Users ON Visits.UserID=Users.UserID;
+	Delete a visit
+		DELETE FROM Visits WHERE VisitID='1';
+		
+Visit detail window:
+	Get committment levels for all faculty for a given visit
+		SELECT VisitID, Users.UserID, Name, Email FROM Visits_Users INNER JOIN Users ON Visits_Users.UserID=Users.UserID WHERE VisitID=2;
+	Find intersection of visit availability with each faculty availability
+		SELECT Users.UserID, Name, Visits.Availability & Users.Availability FROM Visits INNER JOIN Users WHERE VisitID=1;  /* Note that this is using the bitwise and operator "&" because of the way we are storing availability.   */
+	Set email frequency for a particular visit
+		UPDATE Visits SET NotificationFrequency=4 WHERE VisitID=2;
+	Set committment level for a given faculty member
+		INSERT INTO Visits_Users VALUES (1,1,'prefer not');
+	Claim a visit and a time
+		UPDATE Visits SET DecidedTime=4, Status='assigned' WHERE VisitID=1 AND Status='proposed';
+		INSERT INTO Visits_Users VALUES (1,1,'can do') ON CONFLICT (VisitID,UserID) DO UPDATE SET Willingness='can do' WHERE (VisitID,UserID)=(1,1);
+	Update visit details
+		UPDATE Visits SET UserID=1 WHERE VisitID=3;
+User tab:
+	Get list of users, including faculty availability
+		SELECT * FROM Users;
+	Create new user
+		INSERT INTO Users(Name,Email,PasswordHash,IsAdmin,IsFaculty,IsCoordinator) VALUES ('DrKow', 'mkowalcz@nmu.edu', 'secret', TRUE, TRUE, TRUE);
+		INSERT INTO Users(Name,Email,PasswordHash,IsAdmin,IsFaculty,IsCoordinator) VALUES ('Randy', 'rappleto@nmu.edu', 'secret', FALSE, TRUE, FALSE);
+	Update user attributes
+		UPDATE Users SET PasswordHash='secret',IsAdmin=TRUE WHERE Name='DrKow';
+	Update faculty availability
+		UPDATE Users SET Availability=-9223372036854775801 WHERE Email='rappleto@nmu.edu';
+	Delete user
+		DELETE FROM Users WHERE UserID=2;
+	Update global settings
+		UPDATE Settings SET Value='5' WHERE Key='HyperlinkLifetime';
+		UPDATE Settings SET Value='5' WHERE Key='CoordinatorNotificationFrequency';
+
+References:
+	https://stackoverflow.com/questions/7662/database-table-and-column-naming-conventions
+	https://dev.to/ovid/database-naming-standards-2061
+	https://stackoverflow.com/questions/3037188/naming-of-boolean-column-in-database-table
+	https://stackoverflow.com/questions/2300356/using-a-single-row-configuration-table-in-sql-server-database-bad-idea
+	https://www.sqlite.org/foreignkeys.html
+	https://www.sqlite.org/lang.html