I have an entity for which I don't want a table. The entity is used to generate a report and is populated using a SQL query:
public IEnumerable<Entities.MembersReportRow> Get()
{
return _context.MembersReportRows
.FromSqlRaw(#"
SELECT...")
.ToList();
}
Using modelBuilder.Ignore<MembersReportRow>(); stops the code for creating the table from being added to the migration, but then the method above stops working with error:
Cannot create a DbSet for 'MembersReportRow' because this type is not
included in the model for the context.
I've also tried:
modelBuilder.
.HasNoKey()
.ToSqlQuery(#"
SELECT...
");
...but the code to create the table still gets created in the migration, which surprises me a little as I'm specifically stating "ToSqlQuery".
Any help would be appreciated!
Related
I'm looping over a bunch of tables and have to delete records in each of them having a specific column name. I was able to get that list but the following line gives me the exception: Microsoft.Data.SqlClient.SqlException (0x80131904): Must declare the table variable "#p0".
foreach (var dsw in deleteSwModels)
{
contextCtx.Database.ExecuteSqlInterpolated($"DELETE FROM {dsw.Name} WHERE DeleteSw = 1");
}
The property Name looks like Person.Address where Person is the schema name under which the table is placed.
The version of Entity Framework Core is 3.1.8
I went digging further into the exception details and in the source code at Github ef core.
I solved the problem by making use of the following statement instead:
contextCtx.Database.ExecuteSqlRaw($"DELETE FROM {dsw.Name} WHERE DeleteSw = 1");
I hope it helps someone else in the future.
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.
My application uses Entity Framework 5.0 code-first on top of a Sql CE database. Until now, we have used Automatic Migrations to manage entity mapping changes. However, I now have a change for which I need to create a custom migration to ensure no data is lost during the update. I made my changes to the entities, and used the Add-Migration command which generated Up() and Down() methods for me. I customized the Up() method to insert my custom sql to preserve the data, and tested my application.
When I run the application, I received the error:
Unable to update database to match the current model because there are pending changes and automatic migration is disabled. Either write the pending model changes to a code-based migration or enable automatic migration. Set DbMigrationsConfiguration.AutomaticMigrationsEnabled to true to enable automatic migration.
Ok, I don't understand this because all of my changes are detailed in the Up() method that got executed.
So I turn Automatic Migrations back on just to see what happens. Now I receive this error:
"Cannot alter column of type NTEXT or IMAGE [ Column Name = LastName ]"
This error comes from a table/entity that hasn't even been touched with my changes. The existing database has this string mapped to nvarchar(4000). If I examine the DB after I receive this exception, I observe that the columns have been changed to ntext. What is EF doing? Why is it touching tables that haven't been changed? How can I get more information on what is going on here?
Update:
As a workaround, I attempted to mark each and every string type in my entities with a data annotation as such:
[Column(TypeName = "ntext")]
public virtual string LastName
{
get;
set;
}
Now all of my strings are using ntext in the database. This leads to further exceptions when queries are performed:
The ntext and image data types cannot be used in WHERE, HAVING, GROUP BY, ON, or IN clauses, except when these data types are used with the LIKE or IS NULL predicates.
So, to summarize:
Turning off automatic migrations causes EF to detect phantom changes and throw exceptions
Turning on automatic migration in conjunction with a custom migration causes all existing strings to be mapped to ntext
strings mapped to ntext cannot be queried, effectively making them useless in my application
For me, a modification of an Up method worked out.
SerialNumber = c.String(maxLength: 99)
was applied instead of
SerialNumber = c.String()
i had the same issue and i fixed by editing the table column data type manually by opening SQl Server Compact/SQlite Toolbox explorer windows, and then expend the database name, then expend the table you want to edit and right click the column you want to edit, and click drop script, then run the scrip and the column will be dropped from the table, then right click the table and click add column and from here you can choose what data type you want and add the new column that way. I hope this helps some one.
Now i'm using EF6 Alpha, and when using migration, it will add a new migration log into the __MigrationHistory table.
In EF6, The __MigrationHistory table has a new column called "ContextKey". After testing, I found there are two default "ContextKey" value:
The full name of DbContext's derived class.This happens when i run the code:
Database.CreateIfNotExists();
The full name of DbMigrationsConfiguration's derived class. This happens when i run the code:
public ArticleDbContext()
{
Database.SetInitializer(new MigrateDatabaseToLatestVersion<ArticleDbContext, ArticleConfiguration>());
}
The first time i run the application, "Database.CreateIfNotExists();" create a new database for me, also all tables that map to the models defined in ArticleDbContext, and then add a __MigrationHistory row which ContextKey's value is "Module.Article.Model.ArticleDbContext".
And then "Database.SetInitializer(new MigrateDatabaseToLatestVersion());" will be runned, this code will generate a new ContextKey "PowerEasy.Module.Article.Migrations.ArticleConfiguration". Migration query the __MigrationHistory table with this ContextKey and find out there's no data. So again it will create all tables that map to the models defined in ArticleDbContext, but the tables are already exist in the database, so an exception will be throwed, and tell me "the table XXX is already existed".
How can i solve this?
You should not mix Migrations and the Database.CreateIfNotExists method (or any of the initializers built on top of it). Migrations will take care of creating the database if it does not already exist.
As an alternative to the Migrations initializer, you can also apply migrations using the DbMigrator.Update method. This is useful if you want to create/update the database before it would otherwise be triggered by the initializer.
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;