Is it possible to retrieve records from a view that has not been defined in the model and to retrieve his columns value by using column name or ordinal ?
I write this code :
AppContext ctx = new AppContext("name=DbConnString");
string commandText = "SELECT V.ID, V.Code, V.Description FROM vw_UserDefinedView AS V";
ObjectQuery<DbDataRecord> query = new ObjectQuery<DbDataRecord>(commandText, ctx);
but an exception occurred when I try to execute it :
'vw_UserDefinedView' could not be resolved in the current scope or context. Make sure that all referenced variables are in scope, that required schemas are loaded, and that namespaces are referenced correctly. Near simple identifier, line 1, column 43.
Is there a way to accomplish this using Entity Framework and ObjectContext (or DbContext) ?
Best regards,
Alberto
No, this is not possible. As the message already states: "'vw_UserDefinedView' could not be resolved in the current scope or context." This view is not known to the context (.edmx). You have to realize that you are querying the Entity Model and not the Database!
If you don't want this view (for whatever reason) in your Entity Model, then simply use SqlCommand, SqlConnection and SqlDataReader to execute your statements concerning vw_UserDefinedView.
UPDATE
Maybe this link can help you further: Entity Framework : Add Properties/Entities during runtime
Related
I get the error "Cannot insert explicit value for identity column in table 'UserPermission' when IDENTITY_INSERT is set to OFF" trying to insert a record as follows:
dbContext.User.Add(someUser);
dbContext.SaveChanges();
That being said, the User file has the custom class UserPermission as one of its parameters, and someUser's UserPermission is not null and has a set ID parameter. Why does this happen and is it possible to avoid getting this error without having to explicitly add a UserPermissionID foreign key parameter in my User model and setting the UserPermission parameter to null?
Thanks in advance.
This issue typically happens when deserializing entities that have related entities in the object graph then attempting to add them. UserPermission is likely an existing record that in the DB is set up with an identity PK, but EF doesn't appear to recognize that in the entity definition. (I.e. set to DatabaseGenerated(DatabaseGeneratedOption.Identity). If it had been you would most likely be seeing a different problem where a completely new duplicate UserPermission was being created.
If someUser, and it's associated someUser.UserPermission are deserialized entities then you need to do a bit of work to ensure EF is aware that UserPermission is an existing row:
void AddUser(User someUser)
{
var existingPermission = _context.UserPermissions.Local
.SingleOrDefault(x => x.UserPermissionId == someUser.UserPermission.UserPermissionId);
if (existingPermission != null)
someUser.UserPermission = existingPermission;
else
_context.Attach(someUser.UserPermission);
_context.Users.Add(someUser);
_context.SaveChanges();
}
In a nutshell, when working with detached entities that a DbContext may not be tracking, we need to check the Local state for any existing tracked instance for that ID. If we find one, we substitute the detached reference for the tracked one. If we don't find one, we attach the detached one before Adding our user.
This still isn't entirely safe because it assumes that the referenced UserPermission will exist in the database. If for any reason a non-existent UserPermission is sent in (row deleted, or fake data) you will get an exception on Save.
Passing detached entity references around can seem like a simple option at first, but you need to do this for every reference within a detached entity. If you simply call Attach without first checking, it will likely work until you come across a scenario where at runtime it doesn't work because the context happens to already be tracking an instance.
I have a legacy database with a particular table -- I will call it ItemTable -- that can have billions of rows of data. To overcome database restrictions, we have decided to split the table into "silos" whenever the number of rows reaches 100,000,000. So, ItemTable will exist, then a procedure will run in the middle of the night to check the number of rows. If numberOfRows is > 100,000,000 then silo1_ItemTable will be created. Any Items added to the database from now on will be added to silo1_ItemTable (until it grows to big, then silo2_ItemTable will exist...)
ItemTable and silo1_ItemTable can be mapped to the same Item entity because the table structures are identical, but I am not sure how to set this mapping up at runtime, or how to specify the table name for my queries. All inserts should be added to the latest siloX_ItemTable, and all Reads should be from a specified siloX_ItemTable.
I have a separate siloTracker table that will give me the table name to insert/read the data from, but I am not sure how I can use this with entity framework...
Thoughts?
You could try to use the Entity Inheritance to get this. So you have a base class which has all the fields mapped to ItemTable and then you have descendant classes that inherit from ItemTable entity and is mapped to the silo tables in the db. Every time you create a new silo you create a new entity mapped to that silo table.
[Table("ItemTable")]
public class Item
{
//All the fields in the table goes here
}
[Table("silo1_ItemTable")]
public class Silo1Item : Item
{
}
[Table("silo2_ItemTable")]
public class Silo2Item : Item
{
}
You can find more information on this here
Other option is to create a view that creates a union of all those table and map your entity to that view.
As mentioned in my comment, to solve this problem I am using the SQLQuery method that is exposed by DBSet. Since all my item tables have the exact same schema, I can use the SQLQuery to define my own query and I can pass in the name of the table to the query. Tested on my system and it is working well.
See this link for an explanation of running raw queries with entity framework:
EF raw query documentation
If anyone has a better way to solve my question, please leave a comment.
[UPDATE]
I agree that stored procedures are also a great option, but for some reason my management is very resistant to make any changes to our database. It is easier for me (and our customers) to put the sql in code and acknowledge the fact that there is raw sql. At least I can hide it from the other layers rather easily.
[/UPDATE]
Possible solution for this problem may be using context initialization with DbCompiledModel param:
var builder = new DbModelBuilder(DbModelBuilderVersion.V6_0);
builder.Configurations.Add(new EntityTypeConfiguration<EntityName>());
builder.Entity<EntityName>().ToTable("TableNameDefinedInRuntime");
var dynamicContext = new MyDbContext(builder.Build(context.Database.Connection).Compile());
For some reason in EF6 it fails on second table request, but mapping inside context looks correct on the moment of execution.
None of the many questions on this topic seem to match my situation. I have a large data model. In certain cases, only a few of the fields need be displayed on the UI, so for those I replaced the LINQ to Entity query that pulls in everything with an Entity SQL query retrieving only the columns needed, using a Type constructor so that I got an entity returned and not a DbDataRecord, like this:
SELECT VALUE MyModelNameSpace.INCIDENT(incident.FieldA, incident.FieldB, ...) FROM ... AS ...
This works and displays the fields in the UI. And if I make a change, the change makes it back to the entity model when I tab out of the UI element. But when I do a SaveChanges, the changes do not get persisted to the database. No errors show up in the Log. Now if I very carefully replace the above query with an Entity Sql query that retrieves the entire entity, like this:
SELECT VALUE incident FROM MyDB.INCIDENTs AS incident...
Changes do get persisted in the database! So as a test, I created another query like the first that named every column in the entity, which should be the exact equivalent of the second Entity SQL query. Yet it did not persist changes to the database either.
I've tried setting the MergeOption on the returned result to PreserveChanges, to start tracking, like this:
incidents.MergeOption = MergeOption.PreserveChanges;
But that has no effect. But really, if retrieving the entire entity with Entity Sql persists changes, what logical purpose would there be for behaving differently when a subset of the fields are retrieved? I'm wondering if this is a bug?
Gert was correct, the problem was that the entity was not attached. Dank U wel, Gert! Ik was ervan verbluft!
I just wanted to add a little detail to show the full solution. Basically, the ObjectContext has an Attach method, so you'd think that would be it. However, when your Entity SQL select statement names columns, and you create the object using a Type as I did, the EntityKey is not created, and ObjectContext.Attach fails. After trying and failing to insert the EntityKey I created myself, I stumbled across ObjectSet.Attach, added in Entity Framework 4. Instead of failing, it creates the EntityKey if it is missing. Nice touch.
The code was (this can probably be done in fewer steps, but I know this works):
var QueryString = "SELECT VALUE RunTimeUIDesigner.INCIDENT (incident.INCIDENT_NBR,incident.LOCATION,etc"
ObjectQuery<INCIDENT> incidents = orbcadDB.CreateQuery<INCIDENT>(QueryString);
incidents.MergeOption = MergeOption.PreserveChanges;
List<INCIDENT> retrievedIncidents = incidents.ToList<INCIDENT>();
orbcadDB.INCIDENTs.Attach(retrievedIncidents[0]);
iNCIDENTsViewSource.Source = retrievedIncidents;
I have the code below (this is actually part of a much more complicated query, but I have isolated the issue to this particular line to help with debugging) which per everything I have read should create an IN clause in SQL, assuming I am using EF4. As far as I can tell, I am using EF4 (We are using .NET Framework 4 for our projects and when I look at the System.Data and System.Data.Entity they both say version 4.0.0.0 for all the projects)
int[] assessmentIDs; // this is just here to show what this is,
// but it is a params parameter passed to this methed
var assessments = from cert in container.ProctorAssessmentCertifications
where assessmentIDs.Contains(cert.AssessmentID)
select cert.ID;
However, when I run this, I get the runtime error:
LINQ to Entities does not recognize the method 'Boolean Contains[Int32](Int32[], Int32)' method, and this method cannot be translated into a store expression.
When I use LinqPad, it does correctly output an IN clause like one would expect in EF4.
My questions are:
A. What am I doing wrong and how do I make this work?
B. How do I force EF4 to be called if in fact it's not? I can find no reference in any web.config file that point it to the older version.
Contains does not get translated into valid SQL because assessmentIDs is not IQueryable, it is an in-memory object. So you'll have to pull the data out first, and then do the check.
var assessments = (from cert in container.ProctorAssessmentCertifications
select cert.ID).ToList() //no longer IQueryable.
var result = assessments.Intersect(assessmentIDs);
We're using a Function Import in an EF4 model to populate an existing entity in our Model. The entity in the model has a Key field of Id which we're struggling to map as our stored procedure doesn't return an Id field. I've tried setting the value in the mapping to a literal value of 0 but that fails with an EntityCommandExecutionException and the following exception text.
The data reader is incompatible with the specified 'Candidate'. A member of the type, 'Id', does not have a corresponding column in the data reader with the same name.
Short of modifying the stored procedure to return a dummy Id field can anyone recommend what the best approach is for this as the dummy field option feels very clunky to me.
Many Thanks
If you can't return enough data to fully materialize the entity -- and the Id field is certainly going to be required for that -- then you need to change the return type on the proc to be a complex type instead of an entity.
Use another POCO class with the same structure to receive the results of the stored procedure call, here's an example:
string sp = string.Format("EXEC dbo.spComercialesAsociadosActivos {0}", idComercialPrincipal);
return ((IObjectContextAdapter)this).ObjectContext.ExecuteStoreQuery<InfoComercial>(sp);
In this case "InfoComercial" is a POCO class with the same structure as "Comercial", which is tied up to EF code first in the DBContext, then I used this independent class in the viewModel to create a disconnected "Comercial", it's not an ideal solution but will work fine until EF 5 comes with SP support.