List of questions for identifying the relationships between entities

Questions.txt

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+Q1: When a user changes the company. What happens to the project, resources and tasks?
+I assume each company has its own set of project, resources and tasks and doesn't overlap
+with other companies (p, r, t) ?
+
+i.e a project, resource and task belong to a single company. Is this understanding correct?
+
+Clarification: Projects have a many to one relationship with a Company and Tasks have a many to one relationship with a Project.
+i.e. Assume that a project is not shared between companies and a task is not shared between projects.
+
+Q2: I estimate we don't need the scale of google and facebook reaching 1B users for our database
+design, based on some estimate and fair idea about which business ditio is in lets estimate the
+range for the number of users be in range of 100k-10M as of now. So as to scope our discussion.
+What do you think of this estimate?
+
+Clarification: Yes at the moment, that scale is even smaller. But to design a solution for the range that you specified is more than enough.
+
+Q3: There can be many projects inside the company, so the user is shown only a subset of it -
+project he is been assigned/scheduled? So a company might have project p1, p2, p3, p4 etc.
+But user A is scheduled for project p1, p3.
+
+Is this understanding correct? 
+
+Clarification: Yes that is correct. A user will usually work on a subset of projects in a company.
+
+Q4. Similarly, a project can have many tasks, so the user is shown only a subset of these tasks
+or all the tasks?
+
+Clarification: Assume that the user has the ability to pick any of his scheduled projects and any task in the project when he checks in.
+
+Q5. I think resources are company wide entity and can be used across different projects and tasks
+albeit only when free and not used in some other task. Is this understanding correct?
+So the same resource R1 can be shown to user in Project P1 -> task T1 and Project P2 -> task T2?
+If a user select a resource, then should it become unavailble to other users who might have
+that resource scheduled for them?
+
+Clarification: Exactly right.

SchemaAndQueries.txt

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+# LIST OF ENTITIES AND RELATIONSHIPS
+
+1. users(user_id, user_name, email, password) 
+
+2. projects(project_id, project_name, description, location) 
+
+3. tasks(task_id, task_name, description, project_id)
+
+4. resources(resource_id, resource_name)
+
+5. companies(company_id, comapany_name)
+
+6. admins(admin_id, admin_name)
+
+7. user_works_for_company(user_id, company_id)
+
+8. user_scheduled_for_project(user_id, project_id)
+
+9. user_scheduled_for_resources(user_id, resource_id)
+
+10. user_tasks(user_task_id, user_id, task_id, resource_id, check_in_time, check_out_time)
+
+
+# DB QUERIES FOR A TYPICAL TRANSACTION AT DITIO:
+
+Let's say we have a user in table users with following data,
+(1234, "RAHUL", "RAHUL@GMAIL.COM", "HASH_PASSWORD")  
+
+# User logins into the app.
+1.  SELECT * 
+    FROM users
+    WHERE users.email == "RAHUL@GMAIL.COM" and password == "HASH_PASSWORD"
+
+# User chooses a company.
+2.  SELECT company_id, company_name
+    FROM companies
+    WHERE company_id IN (SELECT company_id
+	                     FROM user_works_for_company
+                         WHERE user_id == 1234)
+
+
+
+
+#   If the assumption is correct and there is not an overlap between the project, task and resources
+#   from one company to another. We have a natural partition happening in the tables. 
+
+#   So for example, instead of having a single table project having project details of all the companies 
+#   we can partition the table horizontally pulling out the data for each company into its separate tables
+#   for each company. 
+
+#   User chooses a company from the list of companies they work for, let say company_id = "company_123".
+#   Now we have sharded the database on company_id i.e we have a separate database running for every
+#   company having its own tables with from table numbers [2, 3, 4, 5, 6, 8, 9, 10]
+
+#   we pick the database url to which the subsequent queries should hit, lets say we maintain a cache
+#   server with redis having (key, value) = (company_id, database_server_url)
+#   let say it looks like following,
+#   company_database_map = {
+        "ditioas" : "https://ditioas.mysql.database.azure.com",
+        "company_123" : "https://company_123.mysql.database.azure.com",
+        "vassabank" : "https://vassabank.mysql.database.azure.com",
+    }
+#   so the following queries will go to "https://company_123.mysql.database.azure.com".
+
+# User gets a list of project which are scheduled for them and selects one project.
+3.  SELECT project_name, description, location 
+    FROM projects 
+    WHERE project_id IN (SELECT project_id 
+	                     FROM user_scheduled_for_project 
+	                     WHERE user_id = 1234)
+
+# User gets a list of resources which are scheduled for them and selects one resource.
+4.  SELECT resource_id, resource_name
+    FROM resources
+    WHERE resource_id IN (SELECT resource_id
+                          FROM user_scheduled_for_resources
+                          WHERE user_id = 1234)
+
+# Let say user chooses a project with project_id = "project_123" and resource with resource_id = "resource_123"
+# User get a list of tasks belonging to the chosen project and chooses one task.
+5.  SELECT tasks.task_id, tasks.task_name, tasks.description
+    FROM tasks
+    WHERE tasks.project_id = "project_123"
+    AND tasks.task_id IN (
+        SELECT user_scheduled_for_task.task_id
+        FROM user_scheduled_for_task
+        WHERE user_scheduled_for_task.user_id = 1234
+    );
+
+
+# Let say user chooses a task with task_id = "task_123"
+# User clicks on check-in and records the check-in time.
+6. UPDATE user_scheduled_for_task
+   SET resource_id = "resource_123", checkin_time = '2023-01-25 09:00:00'
+   WHERE user_id = 1234 AND task_id = "task_123"
+
+# User clicks on check-out and records the check-out time.
+7. UPDATE user_scheduled_for_task
+   SET checkout_time = '2023-01-25 11:00:00'
+   WHERE user_id = 1234 AND task_id = "task_123"
+
+
+
+

backend/ApiLayer.cs

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+public class UserController : ControllerBase
+{
+    private readonly IUserService _userService;
+
+    [HttpGet("{userId}/companies")]
+    public IActionResult GetAllCompaniesForUser(int userId)
+    {
+        var companies = _userService.GetAllCompaniesForUser(userId);
+        return Ok(companies);
+    }
+
+    [HttpGet("{userId}/projects")]
+    public IActionResult GetAllProjectsForUser(int userId)
+    {
+        var projects = _userService.GetAllProjectsForUser(userId);
+        return Ok(projects);
+    }
+
+    [HttpGet("{userId}/resources")]
+    public IActionResult GetAllAvailableResourcesForUser(int userId)
+    {
+        var resources = _userService.GetAllAvailableResourcesForUser(userId);
+        return Ok(resources);
+    }
+}
+
+public class CompanyController : ControllerBase
+{
+    private readonly ICompanyService _companyService;
+
+    [HttpGet("{companyId}/databaseUrl")]
+    public ActionResult<string> GetDatabaseUrl(int companyId)
+    {
+        var url = _companyService.GetDatabaseUrl(companyId);
+        return Ok(url);
+    }
+}
+
+public class ProjectController : ControllerBase
+{
+    private readonly IProjectService _projectService;
+
+    [HttpGet("{projectId}/tasks")]
+    public ActionResult<List<Task>> GetAllTasksForProject(int projectId)
+    {
+        var tasks = _projectService.GetAllTasksForProject(projectId);
+        return Ok(tasks);
+    }
+}
+
+public class UserTaskController : ControllerBase
+{
+    private readonly IUserTaskService _userTaskService;
+    private readonly IResourceService _resourceService;
+
+    [HttpPost("checkin")]
+    public IActionResult Checkin(int userId, int taskId, int resourceId, DateTime checkInTime)
+    {
+        // on check in user creates a task, with default value for istaskcompleted as false
+        _userTaskService.CreateUserTask(userId, taskId, resourceId, checkInTime);
+        _resourceService.UpdateResourceAvailability(resourceId, resourceAvailable=false);
+        return Ok();
+    }
+
+    [HttpPost("checkout")]
+    public IActionResult Checkout(int userId, int taskId, int resourceId, DateTime checkOutTime)
+    {
+        // Get the usertaskid for user,task,resource combination where taskisnotcompleted
+        int userTaskId = userTaskService.GetUserTaskId(userId, taskId, resourceId, taskCompleted=false);
+
+        // Update the task as completed, record the checkout time and set the resource available
+        userTaskService.UpdateUserTaskCompletion(userTaskId, checkOutTime, taskCompleted=true);
+        resourceService.UpdateResourceAvailability(resourceId, resourceAvailable=true);
+        return Ok();
+    }
+}

backend/Models.cs

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+public class User
+{
+    public int UserId { get; set; }
+
+    public string UserName { get; set; }
+
+    public string UserEmail { get; set; }
+
+    public string Password { get; set; }
+
+    public List<UserWorksForCompany> UserWorksForCompany {get; set;}
+
+    public List<ProjectScheduledForUser> ProjectScheduledForUser {get; set;}
+
+    public List<ResourceScheduledForUser> ResourceScheduledForUser {get; set;}
+}
+
+public class Company
+{
+    public int CompanyId { get; set; }
+
+    public string CompanyName { get; set; }
+
+    public string CompanyDatabaseUrl { get; set; }
+
+    public List<UserWorksForCompany> UserWorksForCompany {get; set;}
+
+    public List<Project> Project {get; set;}
+
+    public List<Resource> Resource {get; set;}
+}
+
+public class UserWorksForCompany
+{
+    public int UserId { get; set; }
+
+    public string CompanyId { get; set; }
+
+    public User User { get; set; }
+
+    public Company Company { get; set; }
+}
+
+public class Project
+{
+    public int ProjectId { get; set; }
+
+    public string ProjectName { get; set; }
+
+    public string ProjectDescription { get; set; }
+
+    public List<ProjectScheduledForUser> ProjectScheduledForUser {get; set; }
+
+    public Company Company {get; set;}
+
+    public List<Task> Task;
+}
+
+public class ProjectScheduledForUser
+{
+    public int ProjectId { get; set; }
+
+    public int UserId {get; set;}
+
+    public Project Project {get; set;}
+
+    public User User {get; set;}
+}
+
+public class Resource
+{
+    public int ResourceId { get; set; }
+
+    public string ResourceName { get; set; }
+
+    public bool ResourceAvailable { get; set; }
+
+    public Company Company {get; set;}
+
+    public List<ResourceScheduledForUser> ResourceScheduledForUser;
+}
+
+public class ResourceScheduledForUser
+{
+    public int ResourceId { get; set; }
+
+    public int UserId {get; set;}
+
+    public Resource Resource {get; set;}
+
+    public User User {get; set;}
+}
+
+public class Task
+{
+    public int TaskId { get; set; }
+
+    public string TaskName { get; set; }
+
+    public string TaskDescription { get; set; }
+
+    public Project Project {get; set;}
+}
+
+public class UserTask
+{
+    public int UserTaskId { get; set; }
+
+    public int UserId { get; set; }
+
+    public int TaskId { get; set; }
+
+    public int ResourceId { get; set; }
+
+    public bool TaskCompleted {get; set;}
+
+    public DateTime CheckInTime { get; set; }
+
+    public DateTime CheckOutTime { get; set; }
+}

backend/ServiceLayer.cs

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+public interface IUserService
+{
+    List<Company> GetAllCompaniesForUser(int userId);
+
+    List<Project> GetAllProjectsForUser(int userId);
+
+    List<Resource> GetAllAvailableResourcesForUser(int userId);
+}
+
+public interface ICompanyService
+{
+    string GetDatabaseUrl(int companyId);
+}
+
+public interface IProjectService
+{
+    List<Task> GetAllTasksForProject(int projectId);
+}
+
+public interface IResourceService
+{
+    void UpdateResourceAvailability(int resourceId, bool isAvailable);
+}
+
+public interface IUserTaskService
+{
+    void CreateUserTask(int userId, int taskId, int resourceId, DateTime checkInTime);
+
+    int GetUserTaskId(int userId, int taskId, int resourceId, bool taskCompleted);
+
+    void UpdateUserTaskCompletion(int userTaskId, DateTime checkOutTime, bool taskCompleted);
+}
+
+// Client activity sequence for the api calls,
+// 1. userService.GetAllCompaniesForUser()
+// 2. companyService.GetDatabaseUrl()
+
+// subsequent queries will go the the database server with the URL in step2.
+// 3. userService.GetAllProjectsForUser()
+// 4. userService.GetAllAvailableResourcesForUser()
+// 5. projectService.GetAllTasksForProject()
+
+// Check-in
+// 6. userTaskService.CreateUserTask()
+// 7. resourceService.UpdateResourceAvailability(false)
+
+// Check-out
+// 8. userTaskService.GetUserTaskId()
+// 9. userTaskService.UpdateUserTaskCompletion()
+// 10. resourceService.UpdateResourceAvailability(true)
+