I am following Microsoft's guide on how to model data in Cosmos Db. I am trying to implement something based on the second JSON snippet in this section of the guide.
It says:
This model has the three most recent comments embedded in the post
container, which is an array with a fixed set of attributes. The other
comments are grouped in to batches of 100 comments and stored as
separate items. The size of the batch was chosen as 100 because our
fictitious application allows the user to load 100 comments at a time.
From the implementation point of view, posts and comments are separate classes but the partition key is id for posts and postId for comments. The container "post" is the same.
I am using Microsoft.EntityFrameworkCore.Cosmos in a .NET 5.0 app. We have one container called "Users". In my scenario, the user has many logs. Users data is represented by the AppUser entity and the logs data is represented by the Logs entity. I want to store three recent logs in the user document and the rest of the logs of the user in a separate document, just like it is represented in the above example from Microsoft's guide.
So here are my models:
public class AppUser : IdentityUser
{
public AppUser()
{
Logs = new List<Used>();
}
public List<Logs> Logs { get; set; }
}
public class Logs
{
public DateTime Date { get; set; }
public string Details { get; set; }
}
public class LogDocument : Entity
{
public LogDocument() : base("LogDocument")
{
Logs = new List<Logs>();
}
public string UserId { get; set; }
public List<Logs> Logs { get; set; }
}
public abstract class Entity
{
public Entity(string type)
{
this.Id = Guid.NewGuid().ToString();
this.Type = type;
}
/// <summary>
/// Object unique identifier
/// </summary>
[Key]
[JsonProperty("Id")]
public string Id { get; set; }
/// <summary>
/// Object type
/// </summary>
public string Type { get; private set; }
}
The entity configuration in the database context is:
builder.Entity<AppUser>().HasKey(_ => _.Id);
builder.Entity<AppUser>().HasPartitionKey(_ => _.Id);
builder.Entity<AppUser>().Property(_ => _.ConcurrencyStamp).IsETagConcurrency();
builder.Entity<AppUser>().OwnsMany(p => p.Logs);
builder.Entity<LogDocument>().HasKey(e => e.Id);
builder.Entity<LogDocument>().HasPartitionKey(_ => _.UserId)
builder.Entity<LogDocument>().OwnsMany(_ => _.Logs);
builder.Entity<AppUser>().ToContainer("Users");
builder.Entity<LogDocument>().ToContainer("Users");
Whenever I run the application I get the following exception:
InvalidOperationException: The partition key property 'Id' on
'AppUser' is mapped as 'Id', but the partition key property 'UserId'
on 'LogDocument' is mapped as 'UserId'. All partition key properties
need to be mapped to the same store property.
What am I doing wrong? Why should I specify Id as a partition key for LogDocument? If Id is specified as a partition key in the entity configuration of LogDocument, then the error goes away but it is confusing based on how data is represented in the JSON example from Microsoft's guide. There is no key in the comments item. It is just postId and the array of comments.
How would Microsoft's example or my scenario be modelled and configured in a real-world app that uses Microsoft.EntityFrameworkCore.Cosmos?
Related
My current employer is developing a mobile app using Xamarin.Forms and Asp.net mvc on the backend. I suggested to use realm in the mobile app. My manager want to see a POC(Proof of concept) app using realm with backlink feature before allowing it to be used in the app. I am working on the POC on GitHub . The documentation is very limiting and the GitHub repo of realm-dotnet don’t have good sample.
I completed the project. But unable to implement backlink. The sample app I have developed allow user to create assignees(employees) in the first page. The user can delete or edit the employees using context menu. When the user clicks on the employee name the app navigates to the ToDoListPage of that particular employee. Here the user can create ToDoItems. On this ToDoList page I want to show the ToDoItems that where assigned to that employee only.
The models were as follows:
public class Assignee : RealmObject
{
public Assignee()
{
ToDoItems = Enumerable.Empty<ToDoItem>().AsQueryable();
}
[PrimaryKey]
public string Id { get; set; } = Guid.NewGuid().ToString();
public string Name { get; set; }
public string Role { get; set; }
[Backlink(nameof(ToDoItem.Employee))]
public IQueryable<ToDoItem> ToDoItems { get; }
}
public class ToDoItem : RealmObject
{
[PrimaryKey]
public string Id { get; set; } = Guid.NewGuid().ToString();
public string Name { get; set; }
public string Description { get; set; }
public bool Done { get; set; }
public Assignee Employee { get; set; }
}
I am adding employee to each ToDo Item:
Item.Employee = Employee;
_realm.Add(Item);
Now I want to access the ToDoItems for the Employee:
Items = _realm.All<Assignee>().Where(x => x.Id == EmployeeId).FirstOrDefault().ToDoItems;
But this does not work. I will be grateful if someone can help me out by preferably writing code in my sample app or write the correct code in the reply.
Thank you
Firstly, Realm .NET doesn't currently support traversing properties (x.Employee.Id). Due to this, when I start the app and try to go to the ToDoListPage, the app crashes with the exception:
The left-hand side of the Equal operator must be a direct access to a persisted property in Realm
Realm supports object comparison, so we can fix this like so:
var employee = _realm.Find<Assignee>(EmployeeId);
Items = _realm.All<ToDoItem>().Where(x => x.Employee == employee);
Secondly, everything seemed fine in your code, so I dug a bit deeper and saw why it isn't working. The issue is that when we try to get all items with the code above, the EmployeeId parameter is null. Since the EmployeeId is being populated after the load logic has been triggered, we don't need to load the data in the ctor. So you can remove this code.
Finally, since you won't be loading the data in the ctor, and instead in the SetValues method, the UI needs to know, when the data has been updated, what exactly to redraw. Thus, you need to mark the collection to be Reactive too:
[Reactive]
public IEnumerable<ToDoItem> Items { get; set; }
Then, you need to change the SetValues method to use object comparison, instead of traversing:
async Task SetValues()
{
Employee = _realm.Find<Assignee>(EmployeeId);
Title = Employee.Name;
Items = _realm.All<ToDoItem>().Where(x => x.Employee == Employee);
}
To sum up - you don't need to try and load the data in the ctor, since you don't know when the EmployeeId will be set. You are already tracking when the property will change and inside the SetValues command you simply need to change the expression predicate.
I am facing an issue in using SQLite-Net Extensions to save data in local DB in scenario where the foreign key is referencing the same entity (self-join).
Example – Employee and Manager. Every employee has a manager and a manager is also an employee. I am facing issues in saving data in such cases. It will be really helpful if you can provide some insights. Does this extension support this kind of relationship?
Yes, relationships between objects of the same class are supported, but the foreign keys and inverse properties must be explicitly specified in the relationship property attribute because the discovery system will get it wrong as there are be two relationships with the same type.
This example is extracted from the project readme:
public class TwitterUser {
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
public string Name { get; set; }
[ManyToMany(typeof(FollowerLeaderRelationshipTable), "LeaderId", "Followers",
CascadeOperations = CascadeOperation.CascadeRead)]
public List<TwitterUser> FollowingUsers { get; set; }
// ReadOnly is required because we're not specifying the followers manually, but want to obtain them from database
[ManyToMany(typeof(FollowerLeaderRelationshipTable), "FollowerId", "FollowingUsers",
CascadeOperations = CascadeOperation.CascadeRead, ReadOnly = true)]
public List<TwitterUser> Followers { get; set; }
}
// Intermediate class, not used directly anywhere in the code, only in ManyToMany attributes and table creation
public class FollowerLeaderRelationshipTable {
public int LeaderId { get; set; }
public int FollowerId { get; set; }
}
As you can see here we have a many-to-many between Twitter users. In your case it will be a one-to-many, so you won't need the intermediate table and you'll need the foreign key (ManagerId for example) in your Person class.
I have built a new Web Application that uses the template Visual Studio provides and included MVC and Web API. The default authorization mechanism is Identity and the database interaction is done using Entity Framework with Code-first method of creating the database.
I have three requirements:
A user can have a list of Children objects
I do not want to use a "relationship" object
All users already exist on the AspNetUsers table, because they all need to be able to login, so I do not want another table to maintain user data
In theory, multiple parents could have reference to multiple children, but for this example, we will just consider it a one-to-many relationship.
In my application, I need to have an ApplicationUser have a list of ChildUsers as a collection of ApplicationUser such as shown below.
public class ApplicationUser : IdentityUser
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string AddressLine1 { get; set; }
public string AddressLine2 { get; set; }
public string City { get; set; }
public string State { get; set; }
public string PostalCode { get; set; }
public string ShirtSize { get; set; }
public ICollection<ApplicationUser> Children { get; set; }
}
I want these users to be accessible as shown above (a collection of ApplicationUser), not a collection of Relationship object that ties them together such as:
public class Relationship
{
public String ParentId { get;set; }
public String ChildId { get;set; }
}
Can a new table be created and exist on the database without having a code-first model for it to know how to create a relationship table?
What are available solutions to this problem?
After some research, and experimentation, I have found bits and pieces of guidance to arrive at a solution that works.
In order for an intermediate table to be created to maintain the relationship, the ApplicationDbContext OnModelCreating function needs to know what it should look like. I have told it to create a new table that is not bound to an object by using the modelBuilder shown in the code below. Unfortunately, I do not have the links to the articles that guided me to this.
public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
public ApplicationDbContext()
: base( "DefaultConnection", throwIfV1Schema: false )
{
}
public static ApplicationDbContext Create()
{
return new ApplicationDbContext();
}
protected override void OnModelCreating( DbModelBuilder modelBuilder )
{
base.OnModelCreating( modelBuilder );
modelBuilder.Entity<ApplicationUser>()
.HasMany( p => p.ChildUsers )
.WithMany()
.Map( m =>
{
m.MapLeftKey( "Father_Id" );
m.MapRightKey( "Son_Id" );
m.ToTable( "father_son_relation" );
} );
}
}
Additionally, when you need to add Children to the parent ApplicationUser, you will need to do some tweaking as you are about to insert so that it updates the database correctly. I definitely want the UserManager to do the creation of the user for me, but that means that when I go to add the user to my list of Children with the code below, it tries to add it again and throws an exception because it already exists.
var result = await UserManager.CreateAsync( user, model.Password );
var myUserId = User.Identity.GetUserId();
var users = AppDbContext.Users.Where( u => u.Id == myUserId ).Include( u => u.ChildUsers );
var u2 = users.First();
u2.ChildUsers.Add( user );
await AppDbContext.SaveChangesAsync();
After finding this question, I researched the EntityStates and found that adding the following line before calling SaveChanges resolved the exception and it no longer attempts to add it again.
AppDbContext.Entry( user ).State = EntityState.Unchanged;
TADA!!! Now to select them from the database using EF, you can then use the following code:
AppDbContext.Users.Where( u => u.Id == myUserId ).Include( u => u.Children ).First();
Since I am only getting one level of Children this will work ok, after that you risk circular references.
Comments and ideas to improve the code are welcome.
I have the following domain model:
public class Campaign
{
public virtual long Id { get; set; }
public virtual string Name { get; set; }
public virtual ICollection<Content> Content { get; set; }
}
public class Content
{
public virtual long Id { get; set; }
public virtual string Body { get; set; }
}
This is configured:
modelBuilder.Entity<Campaign>().HasMany(x => x.Content).WithOptional();
In my service I have the following code:
Campaign campaign = campaignRepository.GetById(id);
This loads the campaign and any associated content items into the collection which is great. The issue comes with the following code:
campaign.Name = "new value";
campaign.Content.Clear();
unitOfWork.Commit();
This does not delete the content rows from the database. It actually sets the foreign key in the content table to null for the affected rows but it does not delete the rows.
I then tried to modify the configuration to:
modelBuilder.Entity<Campaign>().HasMany(x => x.Content).WithRequired();
This would simply give me the following exception: A relationship from the 'Campaign_Content' AssociationSet is in the 'Deleted' state. Given multiplicity constraints, a corresponding 'Campaign_Content_Target' must also in the 'Deleted' state.
There must be a way to delete rows from the content collection. I must be missing something. Any help is appreciated.
You will have call the Remove method on the corresponding DbSet for each entity instance.
foreach(var content in campaign.Content)
{
dbContext.Contents.Remove(content);
}
I have the following class:
public class User
{
public Guid Id { get; set; }
public string Name { get; set; }
public Couple Couple { get; set; }
}
public class Couple
{
public Guid Id { get; set; }
public User Groom { get; set; }
public User Bride { get; set; }
}
Important points:
Bride and Groom properties are required
One-to-one relationship
In the User class, it is Couple required
DbContext in OnModelCreating
modelBuilder.Entity<User>().HasRequired(u => u.Couple).WithRequiredPrincipal();
modelBuilder.Entity<Couple>().HasRequired(u => u.Bride).WithRequiredDependent();
modelBuilder.Entity<Couple>().HasRequired(u => u.Groom).WithRequiredDependent();
But I can not be required!
All fileds are with null in the database!.
How do I get the fields in the database as not null?
If possible using the API Flient.
It should be this :
modelBuilder.Entity<User>().HasRequired(u => u.Couple).WithRequiredDependent();
modelBuilder.Entity<Couple>().HasRequired(u => u.Bride).WithRequiredDependent();
modelBuilder.Entity<Couple>().HasRequired(u => u.Groom).WithRequiredDependent();
How WithRequiredDependent Works : Configures the relationship to be required:required without a navigation property on the other side of the relationship. The entity type being configured will be the dependent and contain a foreign key to the principal. The entity
type that the relationship targets will be the principal in the relationship.
Meaning : Let's consider your first line of code here. It creates a foreign key in the entity being configured (User) making it Dependant and making the other side of the relationship (Couple) Principal
Important : Don't you think the configuration you desire will generate a deadlock? I've not tested the code above, but this configuration seems to be a deadlock to me so i'm not sure if EF would allow you to create it. User must need a Couple, and Couple must need that same user i guess.