I'm using entity framework code first to create my tables. Please note - create the tables, not the DB, since I'm working on a hosted environment and I don't have a user that is allowed to create db's.
Committing a DB update works fine, but retrieving data gives the exception:
Exception Details: System.Data.SqlClient.SqlException: Invalid object name 'dbo.EventHosts'.
I've read that it happens because I'm not using EF Code First to create the DB. That's fine, but how do I elegantly solve this?
All the generated tables do not have a prefix like dbo. A solution like this doesn't work, and isn't elegant at all:
[Table("EventHosts", Schema = "")]
Ok, for me issue was that I had a table called dbo.UserState and in C# EF was trying to access dbo.UserStates because of pluralization.
The solution was to put Table attribute above class and specify the exact table name:
[Table("UserState")]
public class UserState
{
[Key]
public int UserId { get; set; }
}
To answer your first question: use the schema created for you by your hosting provider.
To answer your second question: No there is currently no direct way to change the default schema globally because you cannot modify existing conventions or create new conventions. You can try to hack it.
For example you can override OnModelCreating and use reflection to get all DbSet<> properties declared in your context. Than you can just use simple loop on these properties and create ToTable mapping call with name of the property as table name and your custom schema. It will require some playing with reflection to make this work.
Alternatively you can try to do some reusable approach by implementing custom conventions. You can find many different articles about using your own conventions with EF. Some examples:
Custom Conventions in Entity Framework Code First v 4.1
Conventions in Entity Framework 4.1 Final
My high level untested idea is following same principle and create assembly level attribute which will be processed by the convention mechanism and applied on all your entities.
Try to set default schema name to 'dbo' in SQL SERVER.
http://msdn.microsoft.com/en-us/library/ms173423.aspx
On of the reason for this error is the table named "EventHosts" may not Exist or that table is renamed to some other name please check with that..
https://stackoverflow.com/a/12808316/3069271
I had same issue, it was pluralize problem between mapping and db.
Related
I have a specific EF Core 6.x question.
If the SQL table has a column removed. Then EF Core will throw a SqlException saying that it's an invalid column name unless I also update the C# model.
For example,
Create Table User
(
FirstName varchar(200)
,MiddleName varchar(200) null -- tried to remove this column after table is created
,LastName varchar(200)
)
I tried deleting the MiddleName column from the SQL Table. When I run a simple read call using EF Core 6, I get the error.
c# model
public class User
{
public virtual string FirstName { get; set; }
public virtual string? MiddleName { get; set; }
public virtual string LastName { get; set; }
}
var db = new EFDbContext(connectionString);
var data = db.Users.ToList(); // SqlException here after column removal
Is there any way to remove columns from the table without needing to update the c# class as well?
Tried making the C# property MiddleName not virtual.
Update:
In the event that I have an existing application. I would need to modify the c# model even if the codebase doesn't refer to the removed column anywhere. Alternatively, I can decorate the property with [NotMapped] or use the Ignore() method in the modelbuilder.
Both approaches means a rebuild of the assembly is needed and downtime during deployment.
NHibernate's mapping can be done using an XML file and thus all it takes would be a simple config file update.
I can't seem to find anything in EF Core that will reduce the headache of maintaining older codebases when schema changes occur.
EF creates a data model mapping internally to track the database schema and your code models. By removing the column in your database table, your code model no longer matches the database. Hence, the exception occurs.
This is definitely not be the answer you're looking for, but as far as I know EF Core need consistency between the models and the DB schemas to work.
I can think of 2 things here:
Maybe you could benefit from using a different ORM (Did you give Dapper a cahnce)
You might be facing an architectural issue, if there's more than one team working with the same database, and more than one system calling that database, the best way to avoid headaches in the future would be to isolate the data access layer and expose an API that serves all the involved systems.
That way, if the database changes, you just need to re-build the data access layer, no downtime for your clients.
And finally... in my opinion the ideal solution is a combination of both, create a decoupled data access layer, map things there and expose an API with the models your application needs.
The entity model I'm working on is structured with inheritence as per:
public abstract class Line {}
public class WooLine : Line{
public bool wooProperty{ get; set; }
}
public class BooLine : Line
These are both stored in the database in the table Line. And in the database the column wooProperty is NOT NULL and default value (0).
These are maintained in a web app written with Knockout & Breeze. When working with BooLine trying to create a new entity, it throws an exception that I can't insert NULL into column wooProperty.
I set up a profile to trace the query, and it appears that since it's mapped to the Line table, during the Insert EntityFramework reads up all the properties and tries to actually insert NULL into the wooProperty, since it's not present in the Boo model. I'm moderately upset that EF is actively trying to insert NULL to a property I'm not working with...
Anyway. I can't move the wooProperty to the Line model - it belongs in the WooLine model. I'm hoping to solve it by either modifying the metadata in Breeze or forcing the wooProperty onto the saveChanges data. But I can't get breeze to recognize the property in the metadata. I've tried to run
metadataStore.registerEntityTypeCtor(
'BooLine', function () {
this.wooProperty = false;
});
Which almost works - but Breeze maps it as __unmapped value and as such isn't recognized after being recieved by EntityFramework.
I also started playing around with overriding the EFContextProvider and overriding BeforeSaveEntity. Entity is ReadOnly of type BooLine, and I can clearly see WooProperty in the UnmappedProperties, but I have no idea where to go from there... Any ideas?
TLDR in a way; Want to 'trick' entity framework into thinking an unmapped value is mapped when creating an entity.
To summarize my comments I would recommend one of the following:
make your model use TPT inheritance so there is no wooProperty column in the Line table, but in the inherited WooLine table
change your wooProperty column to be nullable and mark the wooProperty property in your entity class as [Required] and let EF take care of reading only "valid WooLines" - this should work if there is also a valid discriminator column for EF to use
We are using EF5.0 in our project and we are supplying the Db Schema name using following code in the OnModelCreatingevent
string schemaName = DbSchema;
modelBuilder.Configurations.Add(new TableMap(schemaName));
But our problem is that the OnModelCreating event is called only once(even if I create context object again) and we need to change the Db Schema name for different databases which we are processing in a loop.
I believe that EF 6.0 has a method like HasDefaultSchema but I am unable to find a way for EF5.0
Is there any way to achieve this?
The cleanest way is probably to use the DbContext's ctor overload that takes model [1]. That way you can create two different configurations (though different only in schema) and switch these as needed.
The model itself is represented by DbModel class and created by DbModelBuilder class. It's almost the same as in OnModelCreating method. You can easily parametrize this.
[1] I suppose you want to use one context. If not, you I would go for different context classes.
I have a column in the database that cannot be null, and I want to set it to have a default value in the database . The problem is that entity framework seems to create a default value itself (for example, int => 0), and completely ignores the default value constraint in the database.
Is there any way to disable this default valuing of entity framework?
I have found that you can decorate your fields with the following attribute.
[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
Natively, Entity framework do not allows this. You have to do some code to it. This answer from another site seems to had solved the problem for many people.
He "hacks" it (as he told) by doing something like that:
public partial class YourEntityClass {
public YourEntityClass() {
this.PropertyNameWithDefaultValue = default(int);
}
}
Note 1 : Someone mention that it may not work in EF4
Personal note : Sorry for my english, I usually speak French.
Sometimes we need to do manually what EF doesn't do automatically for us.
In case using EF 4.1 "Code First", I usually create a separated class DbInitializer derived from IDatabaseInitializer, and in the implementation of the InitializeDatabase method, just call the
context.Database.ExecuteSqlCommand("ALTER TABLE TABLENAME ... ");
Now at the static constructor of the class derived from DbContext, just call the initializer:
Database.SetInitializer(new DbInitializer());
In this way, it's possible to specify any database DML/DDL commands to alter tables/columns just to make sure the DB is like we want.
"Computed" fields in EF are not the same as fields with default values in SQL. A computed field is one that is computed on the server and shouldn't be altered when an object is submitted. If you put a Computed tag on a field, you will get the default when you first create the object, but then you will not be able to change that field later on. So, if you get an entity from the DB make a change to a computed field and then call "saveChanges()" on your entity context, the field will not be altered in the DB.
Better to use EF defaults by setting the Default Value for the attribute in the EDMX editor.
It's a pain in the butt that the EDMX updater can't read the field defaults when there is a one to one mapping between the entity field and the database field.
You can update the EDMX model to change the default value for any column via the Properties window. However, Entity Framework doesn't seem to pickup DEFAULT constraints automatically. Not sure if there is a way to make it do that.
I just started learning Nhibernate and Fluent Nhibernate. I want to specify table name when I create my mapping class.
Entity name in application is "CustomerOrders" but in the oracle database, table name is "CUSTOMER_ORDERS".
I learnt from googling that I can use "WithTable" to specify database table name.
I am not sure how to use it and where as Vs2008 didn't find the method.
Thanks
public class CustomerOrdersMap : IAutoMappingOverride<CustomerOrders>
{
public void Override(AutoMapping<CustomerOrders> mapping)
{
mapping.Table("CUSTOMER_ORDERS");
}
}
WithTable was renamed to Table for the 1.0 release. It was mentioned in the release notes (first bullet point).