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Why can't I read a TEXT attribute from SQLITE TABLE in the application?

I this table in a Sqlite db3:
with data in it which I can read with a simple query in SQLite Studio SQL editor:
Select Testo FROM Contenuto
As you can see i only need the Testo attribute.
When I try to do the same query or try to retrive all the attributes (Id, IDSezione, Indice, Testo), in my xamarin Forms Application, the result have all of them but Testo. (Contenuti is a List of Contenuto objects)
This is my DB method:
public Task<List<Contenuto>> GetContenutoAsync(int idsezione)
{
return Database.Table<Contenuto>().Where(i => i.IDSezione == idsezione).ToListAsync();
}
So I'm wondering what is the problem and if someone can help me.
I thought it was a size limit dimension but it do the same with just a character instead of a long text as I need.
class
[Table(nameof(Contenuto))]
public class Contenuto
{
public int ID { get; set; }
public int IDSezione { get; set; }
public int Indice { get; set; }
public string Testo { get; set; }
}
Thanks, Riccardo

So this is how I resolve my problem:
Originally the Testo attribute of the table was named Contenuto as the table name. Not noticing it, I added the DB to the projects anyway.
I noticed that problem on the first run of the app (thrown an exception since you can use the table name as attribute in query), and edited the DB in the common project.
Doing this will not update the Android/iOS DB linked file.
That was the actual problem in my method I was looking for Testo attribute but was not there.
So when you add the DB as new element to android or iOS projects, remember to set its property to Always copy, doing this will always update the linked DB when the app is built.

Despite I use Take() method, EF Core return all data

I have a view in my DB. I have created model of view and call it with EF Core. There are 16 rows in view. When I call it with EF Core and use Take(10) it returns 10 rows but I look DBSet all rows shows there. For detail here is my code
[Table("my_view", Schema ="dbo")]
public class MyView
{
[Column("id")]
[Key]
public int Id { get; set; }
[Column("name")]
public string Name { get; set; }
}
in my action:
public JsonResult Index()
{
using (var context = new CCContext())
{
var listOfData = context.MyView
.AsQueryable().Take(10).ToList();
return Json(listOfData);
}
}
PS. For some problem I couldn't upload screen of result.(https://m.imgur.com/gallery/xmP3q32)
https://imgur.com/a/xmP3q32

If you mean context.MyView contains all rows, then you are right. Because that is a representation of the table in the DB. However, in your example listOfData should contain only 10 rows. If so, then this is as it should be expected.
If the above does not answer your question, please give some more insight and also, what DB provider are you using with EF?
For clarification:
The data is not there untill you ask a debugger (or code) to fetch it for you. The only reason you see it is because you ask the debugger to show its contents, and therefor it fetches its contents. It wont if you wont ask it to.

Entity Framework - Non Key Relationships

Problem
I have a situation whereby I need to use Entity Framework 6, Code First, with a legacy database structure which cannot be changed. The database has a very generic table which stores text based data alongside some non key data which can be used to relate the record back to another table.
To illustrate:
Assume the Notes table has a model as follows:
[Table("Notes")]
public class Notes
{
[Key]
public int RecordId { get; set; }
[Required]
public string RelatedTableName { get; set; }
[Required]
public int RelatedTableRecordId { get; set; }
[Required]
public string NotesText { get; set; }
}
I then have another model which could look like so:
[Table("Drivers")]
public class Drivers
{
[Key]
public int RecordId { get; set; }
[Required]
public string DriverName { get; set; }
public ICollection<Notes> DriverNotes { get; private set; }
}
There is no foreign key which links the tables. The Drivers table is linked to the Notes table by way of the RelatedTableName and RelatedTableRecordId fields.
I do not have a problem reading data from the database and hydrating the models using entity framework.
The problem I have is that I want to be able to save a new Driver and its newly created Notes in one transaction and have the RelatedTableRecordId field set to the primary key of the Driver.
If a foreign key existed entity framework would know to back fill the property but in this case it doesn't know about the relationship.
Key Points
Database Structure must not change.
Must use Entity Framework 6 Code First
Must be able to use an Execution Strategy.
Require a relationship between non key fields.
Need to be able to persist all data in a single transaction.
What I've Tried
I had a similar issue with Audit type data and solved it by doing something similar to the following (note that this is very pseudo here):
public override int SaveChanges()
{
int changes = 0;
//Disable the current execution strategy as the default ones do not support user instantiated transactions.
this.ContextConfiguration.SuspendExecutionStrategy();
try
{
//Wrap a whole transaction inside an execution strategy so that auditing can be combined with regular saving of changes.
this.ExecutionStrategy.Execute(
() =>
{
using (var transaction = this.Database.BeginTransaction())
{
//Reset the change count so that it doesn't increase each time the transaction fails.
changes = 0;
//Remove any audit records created by previous failed transactions.
this.AuditTableChanges.Local.Clear();
//Evaluate the change tracker to identify entities which will potentially require an audit trail.
var insertedEntities = this.ChangeTracker.Entries().Where(entryEntity => entryEntity.State == EntityState.Added).ToList();
//Save all changes to get identities.
changes = base.SaveChanges();
//Create the audit trail for inserted entities. This step must occur after the initial call to SaveChanges() so that the identities are set.
foreach (DbEntityEntry entryEntity in insertedEntities)
{
//For each inserted record, get the audit record entries and add them
foreach (AuditTableChange auditTableChange in GetAuditRecords(entryEntity, AuditTableChangeType.Insert).Result)
this.AuditTableChanges.Add(auditTableChange);
}
//Save the audit trail for inserted entities.
changes += base.SaveChanges();
//Commit all changes to the database
transaction.Commit();
}
});
}
finally
{
//Re-enable the execution strategy so that other calls can benefit from the retry policy.
this.ContextConfiguration.UnSuspendExecutionStrategy();
}
return changes;
}
This worked fine for the Audit data as the implementation was hidden away in the framework. I do not want my development team to have to do all of the above each time they persist records.
In its simplistic form this is as much as I'd want people to be doing:
public void CreateDriver()
{
using (MyContext context = new MyContext())
{
Drivers driver = new Drivers();
driver.DriverName = "Joe Bloggs";
Notes driverNote = new Notes();
driverNote.RelatedTableName = "Drivers";
driverNote.NotesText = "Some very long text";
driver.DriverNotes.Add(driverNote);
context.Drivers.Add(driver);
context.SaveChanges();
}
}
In a way I want a foreign key which exists in code but not in the database so that entity framework knows to fill in the RelatedTableRecordId field. I've read some articles on hacking the EDMX but this project is purely Code First only.
There are older questions on stack overflow which are similar but relate to older versions of entity framework and don't help much or have as much detail as the above.
I'm hoping that someone may have experienced a similar problem and has an answer which may involve perhaps some custom mapping/metadata or some overrides to entity framework logic.
Any help would be appreciated.
Thanks,
Greg

Entity Framework 5 with Oracle table/view doesn't exist inconsistency?

Any help or advice regarding this issue is greatly appreciated.
I am currently working on a project that requires a change in our data layer from a local MS SQL instance to a hosted Oracle solution.
Previously, we were using Entity Framework (Code-First) to build our data layer. I would like to take the same approach with the new data layer. We have several applications that use this library, so trying to keep the new data layer as close to the same (objects, names, etc.) as the original would be ideal. I know that Code-First is not officially supported by Oracle (a work in progress), but have read where others have had some success. Thus, for these reasons, I am attempting to do the same.
I have created my Oracle EF data layer to match as closely as I can to the original MS SQL EF data layer. The issue that I'm currently having is that when I run a query to retrieve the first or default entity from the data layer, I get the following exception:
Oracle.DataAccess.Client.OracleException: ORA-00942: table or view does not exist
If I use the exact same DbContext instance and instead run a sql query using the DbContext.Database.SqlQuery(sqlString), it works. The reason I mention this is because I've read the "table or view does not exist" error refers to a database permissions issue. That does not appear to be the case this time, since I'm using the exact same connection string in the same connection object. The only difference appears to be in using traditional sql statements versus the DbSet entities (& configurations).
My entities are relatively simple, flat objects.
public class HourlyPrice
{
public DateTime MarketDate { get; set; }
public int HourEnding { get; set; }
public string LocationId { get; set; }
public string LocationName { get; set; }
public decimal? Price { get; set; }
public int IsValid { get; set; }
public DateTime DateInserted { get; set; }
public DateTime? DateUpdated { get; set; }
}
public HourlyPriceConfiguration(string viewName)
{
ToTable(viewName);
HasKey(x => new { x.MarketDate, x.HourEnding, x.LocationName });
Property(x => x.Price).HasPrecision(13, 6);
HasEntitySetName("SourceHourlyPrices");
}
Inside my DbContext, I add the HourlyPriceConfiguration injecting the viewName ...
modelBuilder.Configurations.Add(new HourlyPriceConfiguration(this.viewName));
... and declare my IDbSet as ...
public IDbSet<HourlyPrice> SourceHourlyPrices { get; set; }
When running the code, this works ...
var sql = "select * from " + this.viewName;
var prices = db.Database.SqlQuery<HourlyPrice>(sql);
var price = prices.FirstOrDefault();
... but this ...
var price = db.SourceHourlyPrices.FirstOrDefault();
... produces the "table or view does not exist" error.
Is this just an issue with the Code-First approach, or am I missing something here? When debugging the application, I can see the viewName being passed to the configuration class is the same that is being passed to the sql statement used in SqlQuery. I've tried removing the HasEntitySetName() and changing the IDbSet to the standard HourlyPrices, but that didn't work, either.
Thanks again, in advance.

I would like to confirm that I had the same problem with a table name.
In Oracle if the name is not full UPPER CASE the table/view is not found.

Code First Automatic Migrations is limited to working with the dbo schema only.
https://community.oracle.com/thread/3622163
You can put it in beginning OnModelCreating method of your Context class as a workaround.
if (this.Database.Connection.GetType().Equals(typeof(Oracle.ManagedDataAccess.Client.OracleConnection)))
{
modelBuilder.HasDefaultSchema(new Oracle.ManagedDataAccess.Client.OracleConnectionStringBuilder(this.Database.Connection.ConnectionString).UserID);
}

The ORA-00942 exception is not a permission issue (depends on how you look at it of course); but it means that the table you are querying is not visible to your user.
You may try to explicitly set the name of your schema in your ToTable method call by using the ToTable(tableName, schemaName) implementation and see what happens.

Just wanted to add that I had the same problem after moving the DB to a different schema. I realised that it is critically to have the schema name in upper case when using ToTable(tableName, schemaName).

Optimizing Repository’s SubmitChanges Method

I have following repository. I have a mapping between LINQ 2 SQL generated classes and domain objects using a factory.
The following code will work; but I am seeing two potential issues
1) It is using a SELECT query before update statement.
2) It need to update all the columns (not only the changed column). This is because we don’t know what all columns got changed in the domain object.
How to overcome these shortcomings?
Note: There can be scenarios (like triggers) which gets executed based on specific column update. So I cannot update a column unnecessarily.
REFERENCE:
LINQ to SQL: Updating without Refresh when “UpdateCheck = Never”
http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=113917
CODE
namespace RepositoryLayer
{
public interface ILijosBankRepository
{
void SubmitChangesForEntity();
}
public class LijosSimpleBankRepository : ILijosBankRepository
{
private IBankAccountFactory bankFactory = new MySimpleBankAccountFactory();
public System.Data.Linq.DataContext Context
{
get;
set;
}
public virtual void SubmitChangesForEntity(DomainEntitiesForBank.IBankAccount iBankAcc)
{
//Does not get help from automated change tracking (due to mapping)
//Selecting the required entity
DBML_Project.BankAccount tableEntity = Context.GetTable<DBML_Project.BankAccount>().SingleOrDefault(p => p.BankAccountID == iBankAcc.BankAccountID);
if (tableEntity != null)
{
//Setting all the values to updates (except primary key)
tableEntity.Status = iBankAcc.AccountStatus;
//Type Checking
if (iBankAcc is DomainEntitiesForBank.FixedBankAccount)
{
tableEntity.AccountType = "Fixed";
}
if (iBankAcc is DomainEntitiesForBank.SavingsBankAccount)
{
tableEntity.AccountType = "Savings";
}
Context.SubmitChanges();
}
}
}
}
namespace DomainEntitiesForBank
{
public interface IBankAccount
{
int BankAccountID { get; set; }
double Balance { get; set; }
string AccountStatus { get; set; }
void FreezeAccount();
}
public class FixedBankAccount : IBankAccount
{
public int BankAccountID { get; set; }
public string AccountStatus { get; set; }
public double Balance { get; set; }
public void FreezeAccount()
{
AccountStatus = "Frozen";
}
}
}

If I understand your question, you are being passed an entity that you need to save to the database without knowing what the original values were, or which of the columns have actually changed.
If that is the case, then you have four options
You need to go back to the database to see the original values ie perform the select, as you code is doing. This allows you to set all your entity values and Linq2Sql will take care of which columns are actually changed. So if none of your columns are actually changed, then no update statement is triggered.
You need to avoid the select and just update the columns. You already know how to do (but for others see this question and answer). Since you don't know which columns have changed you have no option but set them all. This will produce an update statement even if no columns are actually changed and this can trigger any database triggers. Apart from disabling the triggers, about the only thing you can do here is make sure that the triggers are written to check the old and new columns values to avoid any further unnecessary updates.
You need to change your requirements/program so that you require both old and new entities values, so you can determine which columns have changed without going back to the database.
Don't use LINQ for your updates. LINQ stands for Language Integrated QUERY and it is (IMHO) brilliant at query, but I always looked on the updating/deleting features as an extra bonus, but not something which it was designed for. Also, if timing/performance is critical, then there is no way that LINQ will match properly hand-crafted SQL.

This isn't really a DDD question; from what I can tell you are asking:
Use linq to generate direct update without select
Where the accepted answer was no its not possible, but theres a higher voted answer that suggests you can attach an object to your context to initiate the change tracking of the data context.
Your second point about disabling triggers has been answered here and here. But as others have commented do you really need the triggers? Should you not be controlling these updates in code?
In general I think you're looking at premature optimization. You're using an ORM and as part of that you're trusting in L2S to make the database plumbing decisions for you. But remember where appropriate you can use stored procedures execute specific your SQL.