I was playing with the azure Document Db and came accross a problem or rather confusing about Ids. I know that DocumentDb generates a "lowercase" "id" property for every document, this is fine with me, but I cant seem to figure out how to get this "id" when using the .net client. my code looks like below
public class Company
{
public Guid Id { get; set; } // this somehow does not get mapped to the "id" in the document.
public string Name { get; set; }
public string Address { get; set; }
}
so when i query like
client.CreateDocumentQuery<Company>(collection.DocumentsLink).ToList();
the id property is not mapped. I think I havent understood the ID concept in document db and how it maps to your entities properly.
Any help is much appreciated.
Try changing your company entity to
[JsonProperty("id")]
public String Id { get; set; }
This will load the documentdb generated Id, into the id field.
Let me know if that doesnt work.
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 have a problem. I created the following class:
public class KnownDevice
{
public int Id { get; set; }
public string Name { get; set; }
public string IP { get; set; }
public string MAC { get; set; }
public string Type { get; set; }
public List<TriangleRegistryObject> triangles { get; set; }
public List<HexagonRegistryObject> hexagons { get; set; }
}
Now, I want to create a Database on the mobile phone itself, so I use the following code to create the table:
database = DependencyService.Get<ISQLite>().GetConnection();
database.CreateTable<KnownDevice>();
But the code crashes on the second line with the error:
System.NotSupportedException: 'Don't know about
System.Collections.Generic.List`1
Now on the internet I found that it is not allowed to add a List to a database, but I need the data in that list, so I have no idea how I can fix this problem. The list can contain arround 25 rows!
Any idea how I can solve this problem?
List<TriangleRegistryObject> is not a valid type for a SQLite database value. Your type of List<TriangleRegistryObject> does not match any of the clrType == typeof(XXXX) statements, so you get that exception. You will need to rethink the class structure a little to be able to use SQLite-net like that.
For more details about the SQLite database, you could download the source file from the link for reference.
https://learn.microsoft.com/zh-cn/samples/xamarin/xamarin-forms-samples/todo/
If you want to use ou could use List, you could use SQLite-Net Extensions instead of SQLite.
You could refer to the link. The SQLite-Net Extensions library direct to specific relationships in database.
How can you store lists of objects in SQLite.net?
I have a problem with an SQLite database in my Xamarin.Forms PCL project.
I have followed this example from Microsoft Docs:
https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/databases
I've been using my own types to store data and it's worked Ok for simple custom types, but I've recently added List<int> and Attendance type to the custom object (Info).
Now when I try and create the object, i get the following errors:
Don't know about System.Collections.Generic.List`1[System.Int32]
Don't know about MyApp.Attendance
Here is the init code:
readonly SQLiteAsyncConnection database;
database = new SQLiteAsyncConnection(dbPath);
database.CreateTableAsync<UserPrefrences>().Wait();
database.CreateTableAsync<Attendance>().Wait();
database.CreateTableAsync<Info>().Wait();
I'm using Xamarin.Forms with Xamarin.iOS.
You can not store them by default like that. However there is sqlite-net-extensions which you can use to accomplish that. You can take a look about sqlite-net-extensions here.
Using this extension you will be able to do that with TextBlob property, something like this:
public class Address
{
public string StreetName { get; set; }
public string Number { get; set; }
public string PostalCode { get; set; }
public string Country { get; set; }
}
public class Person
{
public string Name { get; set; }
[TextBlob("PhonesBlobbed")]
public List<string> PhoneNumbers { get; set; }
[TextBlob("AddressesBlobbed")]
public List<Address> Addresses { get; set; }
public string PhonesBlobbed { get; set; } // serialized phone numbers
public string AddressesBlobbed { get; set; } // serialized addresses
}
More explanation about TextBlob from url.
Text blobbed properties Text-blobbed properties are serialized into a text property when saved and deserialized when loaded. This allows
storing simple objects in the same table in a single column.
Text-blobbed properties have a small overhead of serializing and
deserializing the objects and some limitations, but are the best way
to store simple objects like List or Dictionary of basic types or
simple relationships.
Text-blobbed properties require a declared string property where the
serialized object is stored.
I just saw that there is also similar/same questions about this topic on StackOverflow already, so you can take a look at them also.
How can you store lists of objects in SQLite.net?
Can I use a List of String in a class intended for SQLite?
This is what my models looks like
public User
{
public string Id { get; set; }
public string Username { get; set; }
public virtual Group Group { get; set; }
}
public Group
{
public string Id { get; set; }
public string Name{ get; set; }
public virtual ICollection<User> Users { get; set; }
}
I using Azure Mobile TableController which using OData for CRUD.
Now I trying to insert new user by specifying the id of the group but instead it gives me an error which shows that instead of trying to associate it with my user model it trying to create new one:
{
"message": "The operation failed due to a conflict: 'Violation of PRIMARY KEY constraint 'PK_dbo.Groups'. Cannot insert duplicate key in object 'dbo.Groups'. The duplicate key value is (ad934511a82c4b42ae5427b5228737c6).\r\nThe statement has been terminated.'."
}
This is what my post looks like:
POST http://localhost/tables/user?ZUMO-API-VERSION=2.0.0 HTTP/1.1
{
email: 'test#test.com',
password: '#test',
group: {
id: 'ad934511a82c4b42ae5427b5228737c6'
}
}
Relationships are not directly supported in Azure Mobile Apps, but you can apply some workarounds to get it to work. Here's a blog post that walks through the scenario: 30 Days of Zumo.v2 (Azure Mobile Apps): Day 26: Relationship Advice.
The specific problem you're running into is the Entity Framework "detatched entities" problem. See e.g. Many to Many Relationships not saving. The problem is that Entity Framework has not loaded the child item into its context, so it thinks that it needs to insert the child item as well as the parent. (There have been long-standing feature requests in Entity Framework to solve this, but the feature has never been added.)
I just posted a similar answer here: How do I insert entities with a 1:n relationship in Azure App Service
Part of my project is to persist data from another source. In this case we have an SAP data source that we will need to pull data from. I need to take the data from SAP and map it to entities I have in my application. Here is an example of an entity I have in my application:
public class Project : BaseEntity
{
public string Name { get; set; }
public string ProjectNumber { get; set; }
public string Description { get; set; }
public string CreatedBy { get; set; }
public string ModifiedBy { get; set; }
public string Currency { get; set; }
#region Navigation Properties
public virtual Address Address { get; set; }
public virtual CompanyCode CompanyCode { get; set; }
public virtual ICollection<Contact> TeamMembers { get; set; }
#endregion
}
As you can see, I have child objects that I map from SAP as well. I need some advice on the best way to insert and update my entities. I am struggling with knowing when to add (insert) entities to my context and when to attach (update) them, because SAP doesn't have knowledge of what my application may or may not have. I need to guard against duplicates, too. For example, should I perform a lookup of each child entity in my parent entity to see if they exist before I apply them to the parent? Then, add / attach the entire parent object to the context or handle each entity separately while still maintaing their relationships?
Yes you must manually test everything to make correct decision what must be inserted, updated or deleted. Depending on the application you can use some more complex queries to reduce number of round trips to the database - for example you can use single query with Contains to load all TeamMembers needed for processed Project or you can load Project with including all related data if you also need to test if project exists.
I did large synchronization application before and I end up with pre-loading all entities at the beginning with few queries and working completely in memory.
Don't forget to use DbSet's Local property or Find method to take advantage of already loaded entities.
You can also use some custom stored procedures to improve performance of this operation.