A table had a fine working _context.update(datarecord) in the Edit post controller.
However, it was decided that instead of updating it, every change should become a new entry.
So _context.add(datarecord)
But thats a problem, since EF is _context aware (you where updating Datarecord.keyxxx)
The key fields are auto generated EF does it for you.
And one may not write a key as keys are protected, which is still fine to me.
There hacks around that, just google :
Cannot insert explicit value for identity column in table 'table' when IDENTITY_INSERT is set to OFF
But why go hacking, why alter the DB table enabling, when that future isn't recommended.
Better leave it to SQL/EF core to generate a new key entry for you.
But then how do I alter the _context to select a new entry.
And be able to add or update that new entry instead?
(when i'm at the Edit controller)
solution is simple EF core accepts :
var mymodel is new MyTable
{
// in here set all model fields except index keys
}
_context.yourdb.Add(mymodel);
Related
I have some Hibernate code running against a Postgres 9.5 DB, which looks like roughly like below (anonymized) -
Integer myEntityId = myEntity.getId();
getCurrentSession().evict(myEntity);
myEntity.setId(null);
MyEntity clonedMyEntity = (MyEntity)getCurrentSession().merge(myEntity);
myEntity.setMyBooleanField(false);
getCurrentSession().save(myEntity);
I have an entity myEntity with a large number of fields. I want to create a duplicate of the record with only 1 field value changed. To achieve this, I evict the entity from session, set Primary Key to null, merge it back to session, set the field I want to change, and then save the entity to DB. However, this code (which was working correctly for some time), is not working now. It sees incorrect value for the boolean field I am trying to modify - as a result violating some database constraints. Please help me fix this or suggest a better way to achieve what I am trying.
The error was happening not on adding this record but on add of another record to an audit table, triggered by the addition of this record. A coworker suggested me to use Eclipse Breakpoint view and use the add breakpoint option there and select the ConstraintViolationException class - this helped me to see the error for which trigger was failing and why and accordingly modify the data to suit the database constraint.
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.
I'm brand new to ASP.NET MVC (Literally just two days of learning on the fly). I'm trying to create a website using MVC, however, I've screwed something up in my solution.
I created this table that had foreign key constraints but I initially forgot to set up a primary key on the id field and forgot to set it identity specification to yes. So when I updated my DataModel and brought this table in, it showed every field as being the primary key and it showed the relationship to the other tables. So I went back to the database and changed the id field for the table to be the primary key and identity specification to yes.
I went back to the DataModel, tried to Update Model From Database, went to the refresh tab, expanded the tables, and selected the table I wanted to refresh, then click on "Finish".
The data model appeared to make the changes but it showed the relationships to the other tables twice.
So I thought I'd delete the table (entity) from the DataModel diagrahm and bring the table back in through Update Model From Database. But when I went back to the Update Model From Database...
Under the Add tab, the table isn't under the Tables
Under the Refresh tab, the table is listed, but when I select it and click on "Finish" the table doesn't reaapear in the diagrahm.
In the model browser...
Under Models
Entity Types, The entity isn't listed
Under Associations, The relationships no longer appear (obviously because the entity is gone).
Under Models.Store
Tables/Views, The table is listed.
Constraints, the relationships are shown.
I've tried dragging the table over to the diagrahm from the Model Browser, but that doesn't appear to work.
I've tried to right click in the diagrahm, add Entity but my table doesn't appear as a Base Type.
I've tried to google but I'm coming up with nothing. With this entity missing, I cannot even build my solution. Please help.
Try to delete the entity file and add it again. But you have to name it as previous entity and don't forget to delete the connectionString in web.config before add it.
If you don't know what I am saying just let me know.
Is there a way to force the ID value for a new entity in EF when we have an auto-incrementing ID column, i.e. use SET IDENTITY_INSERT behaviour through EF?
Our requirement is that our create form must always show a new, unique ID for the object we're creating on the empty form before it is filled in or saved. The idea is that this ID can be out read to someone over the phone and then the user can complete and save the form after the call is complete. We could reserve an ID by inserting an empty row into the database there and then, but we have unique columns and FKs; instead I've made a 'next ID' table that we increment with locks for safety, and I test this against the top ID in the object table too to be careful. The idea was to then force the use of this new ID when we write back the entity - but I can't see how to get EF to do it.
Is that possible - is it just something I've missed? I don't think the ID even makes it down to the insert so I don't think manually calling SET IDENTITY_INSERT around the SaveChanges would help.
Or do I have to do something else? I can see alternatives:
Change our ID column to not be an identity and take manual control of it all: there's a table ID inheritance here so this is potentially tricky too.
Separate DB ID and user-visible ID into a separate column, and record our unique ID there.
Empty row to reserve the ID, as above; might need some nullability changes, and amending our data read code to ignore these records.
Thanks! This is EF4 (using an EDMX and generated classes not POCOs), and against SQL Server 2008 in case that matters.
Why not use a Guid as primary key. Nothing to do with auto-increment, no concurrency pitfalls etc. You just create the Guid at the moment you create the form. Hand it over to a caller and fill in the form afterwards. When the form is cancelled, no problem. When the form is finished create the entity with the created Guid set the other values of the entity object, apply it to the (a) context and SaveChanges()...
Alternatives that wont alter your schema
Use EF Transaction
You can call context.SaveChanges() and get the autoincremented primary key. Once the process is completed you can commit the transaction. If the transaction is cancelled or there is an error/exception, you can always rollback so you wont have holes/dirty-data in your rows. I suggest you use the singleton pattern and pass the same transaction/context to whatever methods or screens to complete the process.
Just add an additional status: Draft
Save empty form as draft with saved ID, then proceed to edit the form with the information. Once complete save the form as final/ready. If you wont proceed to save the form, you can always recycle the draft.