Cross posted on MSDN
We use manual code first Entity Framework for System.Data.Sqlite
So when creating a new entity, we manually create the table, the c# object, and add the DbSet to our context.
I have a very simple object created and I am getting this error when trying to query the context. I have checked the column names and data types many times but I don't see a mismatch here. Also there are no foreign key relationships defined even though the fields have id in the name. Just a standalone table.
The weirdest part is that I can add a new entity to the context, save changes, and it will be persisted to the db. However in the next line when trying to retrieve the entities I get The entity set is not defined in the entity container error. I have also noticed that if I hover over an instantiated context, all the other db sets will have the EF SQL such as SELECT EXTENT1.myCol as myCol, but the department_resources set just says {System.Data.Entity.DbSet<department_resource>}.
Any ideas on what the issue is here?
Below are excerpts of my files:
DDL
CREATE TABLE department_resources (
dep_res_key VARCHAR PRIMARY KEY,
department_id INT NOT NULL,
resource_id INT NOT NULL);
department_resource.cs
[Table("department_resources")]
public class department_resource
{
[Key]
public string dep_res_key { get; set; }
public int department_id { get; set; }
public int resource_id { get; set; }
}
MyContext.cs
public class MyContext : DbContext
{
public DbSet<department_resource> department_resources { get; set; }
}
Sample Usage
using (MyContext db = new MyContext())
{
db.department_resources.Add(new department_resource()
{ dep_res_key = "anID",
resource_id = 22,
department_id = 23 }); // Works
db.SaveChanges(); // Also works. Even persists to db
var foo = from r in db.department_resources
select r.resource_id; // Doesn't work. Will error as soon as I try to use foo. Like assigning to a combo box item source. Or even just enumerating the results
var bar = db.department_resources; // Also doesn't work.
}
The issue is with deferred execution. Although you're assigning foo and bar within your using block, they're not getting evaluated until they're actually used, after MyContext has been disposed.
You need to force them to evaluated within your using block. e.g. by converting the results to lists.
Also I notice you've declared them as vars within your using block. They'll need to be defined outside of it to be able to use them outside (perhaps you just did this in your sample to simplify?)
List<int> foo;
List<department_resource> bar;
using (MyContext db = new MyContext())
{
db.department_resources.Add(new department_resource()
{ dep_res_key = "anID",
resource_id = 22,
department_id = 23 }); // Works
db.SaveChanges(); // Also works. Even persists to db
foo = (from r in db.department_resources
select r.resource_id).ToList();
bar = db.department_resources.ToList();
}
From MSDN
the query variable itself only stores the query commands. The actual
execution of the query is deferred until you iterate over the query
variable in a foreach statement. This concept is referred to as
deferred execution
Forcing Immediate Execution
Queries that perform aggregation functions over a range of source elements must first iterate over
those elements. Examples of such queries are Count, Max, Average, and
First. These execute without an explicit foreach statement because the
query itself must use foreach in order to return a result. Note also
that these types of queries return a single value, not an IEnumerable
collection.
You can also force execution by putting the foreach loop immediately
after the query expression. However, by calling ToList or ToArray you
also cache all the data in a single collection object.
Related
couldn't think of any better title for my question, but the situation is really simple: I have my database (created using code first migration), I have my entity, it has two fields that has index contraint so I cannot insert duplicate records when those fields are same.
public class Entity
{
public int Id;
[Index("IndexName"), IsUnique = true, Order = 0]
[MaxLength(50)]
public string Name;
[Index("IndexName"), IsUnique = true, Order = 1]
public Guid CustomId;
}
For a short entity class example I made this (mine looks with more properties, getters, setters ;) )
I try to make this:
<...>
using (var ctx = new EntitiesDbContext())
{
var e1 = new Entity()
{
Name = "Bob",
CustomId = new Guid("068462F1-3557-E711-BA31-028037EC0200")
};
var e2 = new Entity()
{
Name = "Bob",
CustomId = new Guid("068462F1-3557-E711-BA31-028037EC0200")
};
ctx.Entities.Add(e1);
ctx.Entities.Add(e2);
await ctx.SaveChangesAsync(); // I get exception
}
<...>
Everything is fine, I cannot insert two records because of index, but my problem is, that it does not insert any value at all. Is it possible to make this situation, to add at least one value to DB (i.e. e1 object) ?
P.s. The problem came from more complex situation, my example is pretty obvious or stupid, but it shows the idea what I want to achieve. The problem was the system performance I guess, when two records were inserted into context and then when I context tried to save it, I got an exception.
In all versions of Entity Framework, whenever you execute
SaveChanges() to insert, update or delete on the database the
framework will wrap that operation in a transaction.
Source: https://msdn.microsoft.com/en-us/library/dn456843(v=vs.113).aspx
So you have to save every item seperatly because the behaviour of a transaction is to do no changes to your database in case of an error.
ctx.Entities.Add(e1);
ctx.SaveChanges();
ctx.Entities.Add(e2);
ctx.SaveChanges();
What I found interesting, I can check ctx.ChangesTracker object to get entities list that are changed.
So I just did simple check for changes count and if the count was 2 for example, I made those entities state to Unchanged.
ctx.ChangeTracker.Entries().First().State = EntityState.Unchanged
This solved my problem and pain that I was dealing with for several hours.
I have a Entity called "Client", and another Entity called "Card".
A Client may have many Cards.
My Client Entity looks like this:
public class Client{
public virtual ICollection<Card> Cards {get; set;}
}
Now I want to show the Client data in a DataGrid in WPF, and I want to get Cards Count data,so I add a property to Client Entity, which like this:
public class Client{
public virtual ICollection<Card> Cards {get; set;}
public int CardCount
{
return Cards.Count;
}
}
And then I query the data with Linq and Bind to view
var query = from n in db.Clients select n;
When I run the Application, I got a Exception just right on the return Cards.Count; line;
System.ObjectDisposedException
The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.
So how could I correctly get the cards count?
There is a way simpler method than the other answers here show. Please also realize that solutions such as
var client = db.Clients.FirstOrDefault(c=> c.Id = someid); //get a client
if (client != null)
{
cardCount = client.Cards.Count;
}
will cause an issue called Select N+1 problem. Read up on it if interested, but in a nutshell, it means the following:
Because you are not only interested in one exact client, but you want to display N clients, you need to do one (1) query to get just the clients. Then, by doing the FirstOrDefault stuff, you are actually doing one (1) extra db roundtrip to the database per Client record, which results in an additional N * 1 = N roundtrips. What this means that, if you were to just query the Clients without any related data, you could get however many client records you like, in just one query. But by fetching related data to each of them one-by-one, you are doing way too many db roundtrips.
Here is a way to solve this issue, by using joins and projections. You can get all the data you need in a single DB access:
using (var context = GetDbContext())
{
return context.Clients.Select(cli => new YourViewModel
{
Name = cli.FullName,
// Other prop setters go here
CardCount = cli.Cards.Count
}).Skip((page - 1) * pageSize).Take(pageSize).ToList();
}
You might be wondering, what's the difference afterall? Well, here, you are not working with materialized objects, as others call them here, but with a DbContext. By applying the proper LINQ operators to it (note, that this works not just with DbContext, but also with any IQueryable (well obviously not if you call AsQueryable() on an already in-memory collection but whatever)), LINQ to Entities can construct a proper SQL to join the tables and project the results and therefore you fetch all required data in one go. Note that LINQ to Entities IS ABLE to translate the cli.Cards.Count into a proper SQL Count statement.
You can get the count without loading the entities like this:
using (var context = new MyContext())
{
var client = context.Client.Find(clientId);
// Count how many cards the client has
var cardsCount = context.Entry(client)
.Collection(b => b.Cards)
.Query()
.Count();
}
More information on MSDN page.
You get an ObjectDisposedException if you do not materialize the retreived query. In the following case, the query gets executed only when you Access the first time the list from GetNonMaterialized and not before leaving the method. Fact of this the db is disposed because of lost of scope.
public IEnumerable<Client> GetNonMaterialized()
{
return from n in db.Clients select n;
}
In the following case the query is executed before leaving the method.
public IEnumerable<Client> GetMaterialized()
{
return (from n in db.Clients select n).ToList();
}
Always be sure that the query is executed before exiting the scope of a ObjectContext.
If you want to know whether the query is executed and when enalbe Logging of EF.
How can I turn off Entity Framework 6.1 logging?
I'm importing data from a delimited file using LINQ and Entity Framework and in one scenario EF is not populating the key property. The class is:
public class BallastType
{
public int BallastTypeId { get; set; }
public string Name { get; set; }
}
The file contains a header row and a row for each entry. The code to import it is:
var baseDir = AppDomain.CurrentDomain.BaseDirectory;
var seedDataPath = Path.Combine(baseDir, "bin", "SeedData");
var ballastTypesFile = Path.Combine(seedDataPath, "BallastTypes.txt");
var ballastTypes = (from l in File.ReadAllLines(ballastTypesFile).Skip(1)
let x = l.Split('\t').ToArray()
select new BallastType()
{
Name = x[0]
});
context.BallastTypes.AddRange(ballastTypes);
context.SaveChanges();
Running this code inserts all the entities but BallastTypeId is uninitialized (0). If I add ToList after the select...
...select new BallastType()
{
Name = x[0]
}).ToList();
it works as expected and BallastTypeId is populated. One note is that I'm checking this at a breakpoint.
Why does adding ToList cause EF to work as expected? I'm using EF 6.1.3.
Without a .ToList(), ballastTypes is an IQueryable, and is only evaluated when you enumerate it. If you check the values of BallastTypeId after SaveChanges, you are in essence re-running your LINQ statement, and re-reading the contents of the file. This means that the entities you read when looking for the inserted ID are not the ones you inserted into the context.
If you add a .ToList(), then ballastTypes becomes a list instead of an IQueryable, and can be evaluated multiple times.
I am new to entity framework and I have been searching a while for an answer to this question and I can't find anything that directally addresses this.
Here is the problem. I have a table in Oracle. In this table there are 2 fields(there are more but not important to this question). Card_Transaction_Id and Parent_Card_Transaction_ID. The Parent_Card_Transaction_Id field is constrained by the Card_Transaction_Id field and I am using a Oracle sequence via a trigger to populate the Card_Transaction_Id field.
In my code, I am using Entity Framework(Version 5) to connect using the Code First Approach.
The issue is when I try to create a new record. I need to know what the next sequence value is in order to populate the Parent_Card_Transaction_Id. My mapping for card transactions:
public class CardTransactionMap : EntityTypeConfiguration<CardTransaction>
{
public CardTransactionMap(string schema)
{
ToTable("CARD_TRANSACTION", schema);
// Mappings & Properties
// Primary Key
HasKey(t => t.CardTransactionId);
Property(t => t.CardTransactionId)
.HasColumnName("CARD_TRANSACTION_ID")
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
Property(t => t.ParentCardTransactionId)
.HasColumnName("PARENT_CARD_TRANSACTION_ID");
Property(t => t.CardProfileId)
.HasColumnName("CARD_PROFILE_ID");
}
}
The question is - is there any way to get the next sequence number before I save the record?
My current work arround is to use the following method:
public static decimal GetNextCardTransactionSequenceValue()
{
using (var context = new Context(new OracleConnectionFactory().GetConnection()))
{
var sequence = context.Database.SqlQuery<int>("select card_transaction_id from card_transaction").ToList();
return sequence[0];
}
}
Using that method, I get the next value and then just populate my table. This works but I don't like doing it this way. I feel that there must be a better way to do it.
Thanks in advance.
You have to do this by navigation properties.
By fetching the next value from a sequence before actually using it in the same session you create yourself a concurrency issue: another user can increment the index (by an insert) in the time between drawing its next value and assigning it to the child record. Now the child will belong to the other user's record!
If your CardTransaction class has a parent reference like this:
int ParentCardTransaction { get; set; }
[ForeignKey("ParentCardTransaction")]
CardTransaction ParentCardTransaction { get; set; }
you can create a parent and child in one go and call SaveChanges without worrying about setting FK values yourself:
var parent = new CardTransaction { ... };
var child = new CardTransaction { ParentCardTransaction = parent, ... };
SaveChanges();
Now EF wil fetch the new CardTransactionId from the parent and assign it to the FK of the child. So generating and getting the parent Id happens all in one session, so it is guaranteed to be the same value.
Apart from preventing concurrency issues, of course it is much easier anyway to let EF do the heavy lifting of getting and assiging key values.
Create a Stored Procedure or Query that will return you the next Value from the Table here is an Example
SELECT NVL(MAX(card_transaction_id + 1), 0) AS MAX_VAL
FROM card_transaction T;
or Create a Trigger - for OracleDB
Change your table definition to this :
CREATE TABLE t1 (c1 NUMBER GENERATED BY DEFAULT ON NULL AS IDENTITY,
c2 VARCHAR2(10));
as per the information in the link i provided in the comment.
after the update ef will automatically query the value for the id that is inserted, there is no need to fill in the id before the insert. ef will generate an insert sql query without id.
I have two tables Studies and Series. Series are FK'd back to Studies so one Study contains a variable number of Series.
Each Series item has a Deleted column indicating it has been logically deleted from the database.
I am trying to implement a Deleted property in the Study class that returns true only if all the contained Series are deleted.
I am using O/R Designer generated classes, so I added the following to the user modifiable partial class for the Study type:
public bool Deleted
{
get
{
var nonDeletedSeries = from s in Series
where !s.Deleted
select s;
return nonDeletedSeries.Count() == 0;
}
set
{
foreach (var series in Series)
{
series.Deleted = value;
}
}
}
This gives an exception "The member 'PiccoloDatabase.Study.Deleted' has no supported translation to SQL." when this simple query is executed that invokes get:
IQueryable<Study> dataQuery = dbCtxt.Studies;
dataQuery = dataQuery.Where((s) => !s.Deleted);
foreach (var study in dataQuery)
{
...
}
Based on this http://www.foliotek.com/devblog/using-custom-properties-inside-linq-to-sql-queries/, I tried the following approach:
static Expression<Func<Study, bool>> DeletedExpr = t => false;
public bool Deleted
{
get
{
var nameFunc = DeletedExpr.Compile();
return nameFunc(this);
}
set
{ ... same as before
}
}
I get the same exception when a query is run that there is no supported translation to SQL. (
The logic of the lambda expression is irrelevant yet - just trying to get past the exception.)
Am I missing some fundamental property or something to allow translation to SQL? I've read most of the posts on SO about this exception, but nothing seems to fit my case exactly.
I believe the point of LINQ-to-SQL is that your entities are mapped for you and must have correlations in the database. It appears that you are trying to mix the LINQ-to-Objects and LINQ-to-SQL.
If the Series table has a Deleted field in the database, and the Study table does not but you would like to translate logical Study.Deleted into SQL, then extension would be a way to go.
public static class StudyExtensions
{
public static IQueryable<study> AllDeleted(this IQueryable<study> studies)
{
return studies.Where(study => !study.series.Any(series => !series.deleted));
}
}
class Program
{
public static void Main()
{
DBDataContext db = new DBDataContext();
db.Log = Console.Out;
var deletedStudies =
from study in db.studies.AllDeleted()
select study;
foreach (var study in deletedStudies)
{
Console.WriteLine(study.name);
}
}
}
This maps your "deleted study" expression into SQL:
SELECT t0.study_id, t0.name
FROM study AS t0
WHERE NOT EXISTS(
SELECT NULL AS EMPTY
FROM series AS t1
WHERE (NOT (t1.deleted = 1)) AND (t1.fk_study_id = t0.study_id)
)
Alternatively you could build actual expressions and inject them into your query, but that is an overkill.
If however, neither Series nor Study has the Deleted field in the database, but only in memory, then you need to first convert your query to IEnumerable and only then access the Deleted property. However doing so would transfer records into memory before applying the predicate and could potentially be expensive. I.e.
var deletedStudies =
from study in db.studies.ToList()
where study.Deleted
select study;
foreach (var study in deletedStudies)
{
Console.WriteLine(study.name);
}
When you make your query, you will want to use the statically defined Expression, not the property.
Effectively, instead of:
dataQuery = dataQuery.Where((s) => !s.Deleted);
Whenever you are making a Linq to SQL query, you will instead want to use:
dataQuery = dataQuery.Where(DeletedExpr);
Note that this will require that you can see DeletedExpr from dataQuery, so you will either need to move it out of your class, or expose it (i.e. make it public, in which case you would access it via the class definition: Series.DeletedExpr).
Also, an Expression is limited in that it cannot have a function body. So, DeletedExpr might look something like:
public static Expression<Func<Study, bool>> DeletedExpr = s => s.Series.Any(se => se.Deleted);
The property is added simply for convenience, so that you can also use it as a part of your code objects without needing to duplicate the code, i.e.
var s = new Study();
if (s.Deleted)
...