This shows how to set the identity seed.
EF Code First - how to set identity seed?
dataannotations set identity seed value on Primary Key with code first
How do you set the identity increment value using code first?
There is no way to do it.
None of the ways to configure the entities (conventions, attributes, fluent API) allow to do that. You can neither implement it using custom conventions (in short, a custom convention checks the name, attributes, type, containig type or whatever of a column, and then uses fluent API to config the column, or entity). At least up to EF 6.1.1.
The only way to manipulate an identity in SQL Server is by using DBCC CHECKIDENT, but this only allows to change the seed value, and not the increment.
If you want to change the increment you have to drop the column and create it again in the database initializer Seed method. The problem is that you have to drop and create all the keys (PK or FK) related to this column. (This applies up to SQL Server 2014)
You can have a look at this answer where I explain the possible solutions, alternatives and work arounds, which work, and which don't, and a link to vote to get this included in a future release of EF.
Related
I have the below scenario. I am using EF 5 Code first, MVC 4 on VS 2010. I am using the Unit of Work and Repository pattern for my project.
I am not sure if this is possible or not. Kindly suggest.
I have a model class representing a database table. In the model class, I have a property that is decorated as [NotMapped]. I have a Stored Proc that returns data, similar to the model class. However, when I get the data in a List from the SP, it does not contain value for the [NotMapped] column (SP returns data for the [NotMapped] column though). This may be logically correct with respect to EF.
All I want to know is, do we have a way to get data populated for the [NotMapped] column. I want to achieve, CRUD using LINQ (excluding R - Read).
I would recommend to create a separate complex type for the stored procedure results. Otherwise sooner or later you will find yourself writing code to distinguish between entities coming from the DbSet or from the stored procedure. When the come from the stored procedure they can't be used in joins, for example. Or checks whether or not the unmapped property is set.
A very dirty approach could be to have two different contexts. With code first it is possible to have different contexts with different mappings to the same types, with and without the column ignored (if you use fluent mapping, not with data annotations). But that only succeeds if you tell EF not to check the database schema, so using migrations is ruled out as well. I would not do it!! For the same reason as I mentioned above. I would hate to have a type with a property that sometimes is and sometimes isn't set.
I did work on ADO.NET Entity Framework v2 about two years ago. I have faint memories.
Incidentally, I happen to be working in a very secured (for want of a euphemism) environment where a lot of links are blocked and there's not much one can do. It does get in the way of studying and working, more than a bit.
Therefore, I have to rely on this forum for a few basic questions I have to get started again. This time, I am working on Entity Framework 4. Here are my questions.
All these questions relate to the EDM generated entities, i.e. not the Code First model.
1) Is my understanding correct? I can rename any column name in the EDM designer generated model and nothing breaks.
2) Foreign keys are expressed as navigational properties in the generated entity classes. No special consideration is required to maintain foreign key relationships. I recall in version 1 of EF, you had just ID properties and the navigational IQueryable/IEnumerable/EntityCollection/RelatedEnd properties were introduced in version 2. I just need to know if I need to do anything to retain/maintain foreign key relationships and referential data integrity. I assume I don't need to. A confirmation would be nice.
3) What are all the possible ways to execute a stored procedure? I recall -- one way to use ExecuteSQL or something on the Context.Database object, another to use EntityClient API and the third was to specify stored procedure names in the InsertCommand, SelectCommand, etc. thingies in the mapping window of the EDM designer. Is this correct?
4) How do you use those SelectCommand thingies in the mapping window on an entity? Do you just supply the names of the stored procedures or user defined SQL functions?
5) How do I create an entity out of a subset of a table? Do I just create an entity from the table and then delete the columns I don't need from the designer? What happens if there are required (NOT NULL in SQL) values that are not in the subset I choose?
6) How do I create a table out of a query or join of two or more tables.
1) You can rename columns in the designer and nothing should break (if the name is valid)
2) Navigation properties point to related entities. In EF4 foreign keys were added. Foreign key properties basically expose the database way of handling relations. However, they are helpful since you don't have to load related entities just to change relationship - you can just change the key value to the id of the other entity and save your changes
3) Yes. You can either execute the procedure directly - this is for stored procedures that are not related to CUD (Create/Update/Delete) operations. You can map CUD operations to stored procedure as opposed to having EF execute SQL statements it came up with for your CUD operations.
4) I think this is a bit out of scope - you probably can find a lot of blogs with images how to do it. Any decent book on EF should also have a chapter (or two) on this. Post a question to stackoverflow if you hit a specific problem.
5) Remove properties in the designer and then supply default value to the S-Space definition. I believe you cannot do this with the designer. You need to rightclick on the edmx file and open it with the Xml editor and manually edit it. Also see this: Issue in EF, mapping fragment,no default value and is not nullable
6) You can either create a view in the database or you can create entity set using E-SQL in your edmx file (I think this will be read only though) or you may be able to use Entity Splitting. Each of these is probably a big topic itself so I think you should find more about these and come back if you have more specific questions / problems
Is there a way in ef migrations to set the Foreign GUID key to cascade on update?
If I have two db's with a user table and the same user with different primary keys, I would like to set the primary GUID key of one to the other.
Basically I'm trying to avoid having to create another column between them to check for syncing.
There are two problems in this to solve:
How do get desired behaviour of the database and/or code.
How to get EF Migrations to generate the stuff needed (triggers or whatever) for the solution from point 1.
For the first part, I would look into using a trigger. For the second part, creating the trigger with migrations, it can be done by running a raw sql command in the migration step (you have to use a code based migration).
Everything I find through Google refers to Code First so I'm wondering what the Key attribute is actually doing in regards to a Database First design? I'm mainly curious because a lot of the entities contain composite keys so I've been adding the Key annotation to the respective properties, but is this really necessary? And if so, what do I gain from it?
If you're using the database-first workflow (i.e. you have an .edmx file in your solution). Then the Key attribute will have no effect.
However, if you're using the code-first workflow to map to an existing database, the Key attribute tells code first that that property is part of the entity's primary key.
For more info on the different workflows see this video: Visual Studio Toolbox: Entity Framework Part 1
I have some views that I want to use EF 4.1 to query. These are specific optimized views that will not have keys to speak of; there will be no deletions, updates, just good ol'e select.
But EF wants a key set on the model. Is there a way to tell EF to move on, there's nothing to worry about?
More Details
The main purpose of this is to query against a set of views that have been optimized by size, query parameters and joins. The underlying tables have their PKs, FKs and so on. It's indexed, statiscized (that a word?) and optimized.
I'd like to have a class like (this is a much smaller and simpler version of what I have...):
public MyObject //this is a view
{
Name{get;set}
Age{get;set;}
TotalPimples{get;set;}
}
and a repository, built off of EF 4.1 CF where I can just
public List<MyObject> GetPimply(int numberOfPimples)
{
return db.MyObjects.Where(d=> d.TotalPimples > numberOfPimples).ToList();
}
I could expose a key, but whats the real purpose of dislaying a 2 or 3 column natural key? That will never be used?
Current Solution
Seeming as their will be no EF CF solution, I have added a complex key to the model and I am exposing it in the model. While this goes "with the grain" on what one expects a "well designed" db model to look like, in this case, IMHO, it added nothing but more logic to the model builder, more bytes over the wire, and extra properties on a class. These will never be used.
There is no way. EF demands unique identification of the record - entity key. That doesn't mean that you must expose any additional column. You can mark all your current properties (or any subset) as a key - that is exactly how EDMX does it when you add database view to the model - it goes through columns and marks all non-nullable and non-computed columns as primary key.
You must be aware of one problem - EF internally uses identity map and entity key is unique identification in this map (each entity key can be associated only with single entity instance). It means that if you are not able to choose unique identification of the record and you load multiple records with the same identification (your defined key) they will all be represented by a single entity instance. Not sure if this can cause you any issues if you don't plan to modify these records.
EF is looking for a unique way to identify records. I am not sure if you can force it to go counter to its nature of desiring something unique about objects.
But, this is an answer to the "show me how to solve my problem the way I want to solve it" question and not actually tackling your core business requirement.
If this is a "I don't want to show the user the key", then don't bind it when you bind the data to your form (web or windows). If this is a "I need to share these items, but don't want to give them the keys" issue, then map or surrogate the objects into an external domain model. Adds a bit of weight to the solution, but allows you to still do the heavy lifting with a drag and drop surface (EF).
The question is what is the business requirement that is pushing you to create a bunch of objects without a unique identifier (key).
One way to do this would be not to use views at all.
Just add the tables to your EF model and let EF create the SQL that you are currently writing by hand.