I am using the SQLite.Net-PCL library to manage the SQLite database in my UWP app. The documentation says that calling CreateTableAsync is able to add columns to the table if a properly is added to the data model. However, when I add a property, the application throws an exception that says the table does not have a column named . This means that the new column was not created automatically. I am calling CreateTableAsync in the constructor of the class that manages database calls for the table with a repository design pattern.
I think you missed decorations [PrimaryKey, AutoIncrement] for your class model. Please check the following DataTemple class.
public class DataTemple
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; } //primary key
public string Name { get; set; }
public string Age { get; set; }
}
For more detail you could also refer this sample.
I pulled out all of my CreateTableAsync calls from the repository class constructors and moved them into separate Init Tasks so I can properly await. Now I can add columns to any table without problems.
Related
I created a web application and a model. Then I generated a dbcontext class and a database instance. After I built the project, I tried to connect to that database from Server Explorer in Visual Studio, but could not connect.
I tried to test connection but got an error:
This connection cannot be tested because the specified database does not exist or is not visible to the specified user
Whenever I tried to scaffold view or controller I got this error:
Unable to retrieve metadata for ... one or more validation errors were detected during model generation
ModelsTable is based on type TestModel that has no keys defined.
When I created database object in controller class and write query got same error no key defined.
Also made updates on packages and tried again. I think my connection string is correct.
Here is my model.
public class TestModel
{
[Key]
public string ID { get; } = Guid.NewGuid().ToString();
public string AreaName { get; set; }
public bool IsWorking { get; set; }
public string UserName { get; set; }
public DateTimeOffset Time { get; set; }
}
So I could not use scaffolding, Entity Framework and write query.
Here is my dbcontext class.
public class ModelDB : DbContext
{
public ModelDB()
: base("name=ModelDB")
{
}
public DbSet<TestModel> ModelsTable { get; set; }
}
I searched on internet tried founded solutions but did not understand and could not solve. I hope did not ask unnecessary questions. Thanks for your helping.
Are you using Code First? If so I think you need to generate migrations.
In visual studio go to Package Manager Console and run this commands:
Add-Migration "modelClassName"
Update-Database –Verbose
For more information refer to this link: https://msdn.microsoft.com/en-us/library/jj591621(v=vs.113).aspx
You are missing the set; in the field ID.
I am using code first entity framework approach. I have changed the name Plane_EcoClass to Plane_Class property to the table in the database. It is showing with old property name in the db .How can I update the new property name?. Please let me know how to resolve this error.
public class Plane
{
[Key]
public int Plane_id { get; set; }
public string Plane_Name { get; set; }
public string Plane_No { get; set; }
public string Plane_Class { get; set; }
public virtual List<User>Users { get; set; }
}
you need to add a migration and update the database for the change to affect the database. In the package manager console, type something like:
add-migration YourMigrationName
to create the migration. Review the migration code. Be aware that Entity Framework may try to drop the previously named column and add a column for the new name. This can potentially cause data loss. If this is the case and not desired, then you can manually change the code to use the RenameColumn method.
After adding the migration, you can apply it to the database by going back to the package manager console and typing:
update-database
and then hitting enter. At this point, the package manager console will give you some output regarding running migrations and your seed method and then the database should reflect the updated column name
I have ignored a column through fluent API but want to populate that property while executing stored procedure using some logic. But it is not mapping the ignored column property. Please let me know if there is any way to do this in Entity framework code first.
I've faced with the same problem recently. The only solution I found is a class hierarchy:
public class MyEntityBase {
public int Id { get; set; }
}
public class MyEntity: MyEntityBase {
...
}//This class is mapped to DB with a fluent API and does not contain ignored property.
//Also it does not have derivative classes, so EF will not create class inheritance in DB.
public class DerivedEntity: MyEntityBase {
public int IgnoredProperty { get; set; }
}//Use this class while executing stored procedures
P.S. Do not mark class MyEntityBase as ABSTRACT - EF will map this relationship as database inheritance.
I regularly have the following structure:
MyClass
public virtual ICollection<Version> Versions { get; set; }
public virtual Version CurrentVersion { get; set; }
That is, there is a list of stuff, and some class both points to that list, and one specific item in that list - either the current version of many versions, the next upcoming event in a list of events, etc.
In my schema what I'd like to end up with is a Foreign Key pointing from Version to MyClass - that much works out properly. But then I'd like a Foreign Key pointing from MyClass to Version representing the CurrentVersion property, with no Foreign Key pointing back - I don't want the extra storage or bother of telling a Version what MyClass it's the CurrentVersion for, if any. Put another way, I'd like this second relationship to be one-way from MyClass to Version, even though it's one-to-one.
What EF Code First gives me instead is the normal one-to-many on the first property, with the FK from Version to MyClass, but then a full one-to-one relationship on the second property with an FK pointing in both directions - so the underlying schema for Version ends up with MyClass_Id and MyClass_Id1.
So, is there a way to get a one-way relationship in EF Code First without resorting to the Fluent API? It looked like maybe System.ComponentModel.DataAnnotations.Schema.InverseProperty had a shot at it, but it didn't seem to offer a way to say "Don't generate one."
The key is to specify the InverseProperty on the property that points back, so that EF realizes it's to the Many-to-Many, not to the One-to-One.
public class MyClass
{
public int Id { get; set; }
public Version CurrentVersion { get; set; }
public ICollection<Version> Versions { get; set; }
}
public class Version
{
public int Id { get; set; }
[InverseProperty("Versions")]
public Versioned Versioned { get; set; }
}
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.