I'm considering using the Code First approach with Entity Framework.
I like adding triggers to my SQL database on fields like DateAdded and DateModified so that they automatically update with a getdate() as required.
From what I hear this is difficult with EF: Code First, so is there an alternative?
It doesn't have to be difficult (e.g. getdate() default), you just have to know where to inject...
You can include a custom SQL into the 'chain' - via using Seed-ing
or custom Initializer - to do any kind of custom work.
You may have problems with migrations, if you want to do that 'post-creation' - but if you limit all such similar init work while the Db is still empty you should be ok.
Another thing to worry about is various Db providers - as any custom SQL may vary, or support - but if you know what you're targeting you should be ok.
Check this link - Possible to default DateTime field to GETDATE() with Entity Framework Migrations?
Or this one generally about Triggers https://stackoverflow.com/a/5913581/417747
...it might be close to what you need - and get you ideas about how to do some other things.
Related
Is it possible to do any type of programmatic data transformation in Entity Framework 5 Code First migrations?
There is an Sql() method to execute queries, but it has return type void and I don't see any way to get the results of the queries I perform.
Example
I have table Recipe with one-to-many relationship to Ingredient. For various reasons I want to convert this to a Ingredients JSON string property instead. The only approach I can think of is something like this:
Create new column IngredientsJson
For each recipe, query its ingredients, construct a JSON string programmatically and insert into the new column.
Drop the old table Ingredient.
You should use db 'initializer' for what you want - and/ore 'Seed' of a sort (as to where to inject into the EF flow).
You can > take a look at this post with a customized < initializer - that performas both Db Create... and Migrate. It's not cut and paste solution, but mostly works (it was just a fast go at the problem, you'd need to adjust a bit, it has couple fixes below).
MigrateDatabaseToLatestVersion dose only the migration part - and you need seed-ing exposed - or manually wrap that part (the main point is in 'checks' done for different situations - i.e. when to 'engage' into migration - or seeding).
Migration should go first, and db 'creation' kind of doesn't make much sense, except for seeding.
You override Seed (you created) to put any db handling there - you have the DbContext exposed - and you can also call SqlQuery if needed.
How to create initializer to create and migrate mysql database?
I'm using the SQLite provider for Entity Framework 5 but it doesn't support CreateDatabase and thus cannot auto create the database. (Code First)
Is there a way I can obtain the Model schema at runtime so that I can create the SQL "CREATE TABLE" command myself?
If not at runtime, some other way to obtain the schema so I know how to create the table properly?
Thanks!
A) As for obtaining the model schema at runtime part
(all are earlier posts of mine)
See this one How I can read EF DbContext metadata programmatically?
And How check by unit test that properties mark as computed in ORM model?
Also this one for a custom initializer Programmatic data transformation in EF5 Code First migration
Having said that...
The problem I see is where and at what point you actually have the data available.
Actually I'm quite sure you won't be able to do that at any time.
Because to be able to extract that info you need to have a DbContext running - so db has to be constructed etc. etc.
In the initializer maybe - but using different ways to get that info - the above is not available.
B)
The other way would be to go the way of implementing a provider, generator etc. (e.g. this post).
That way you should get all that info just at the right time from the EF/CF itself.
However I haven't played with that much.
For more info you can check the EF source code
This is more of a 'gathered info' so far - in case it helps you get anywhere with it. Not really a solution. I'll add some more tomorrow.
EDIT:
To get the real database metadata, look into the other DataSpace, this should get you to the right place...
(note: things tend to get less exact from here - as obviously there isn't the right official support)
var ssSpaceSet = objectContext.MetadataWorkspace.GetItems<EntityContainer>(DataSpace.SSpace).First()
.BaseEntitySets
.First(meta => meta.ElementType.Name == "YourTableName");
If you look up in debugger, Table property should have the real table name.
However, reflection might be required.
How I can read EF DbContext metadata programmatically?
How check by unit test that properties mark as computed in ORM model?
Programmatic data transformation in EF5 Code First migration
Entity Framework MigrationSqlGenerator for SQLite
http://entityframework.codeplex.com/
Entity Framework - Get Table name from the Entity
ef code first: get entity table name without dataannotations
Get Database Table Name from Entity Framework MetaData
http://www.codeproject.com/Articles/350135/Entity-Framework-Get-mapped-table-name-from-an-ent
We're using a very basic JPA implementation that should create tables consistently from our models.
I believe we're using EclipseLink or TopLink (whichever one is default with the latest Netbeans/Glassfish). The problem is, the tables are created with inconsistent capitaliztion and with the columns out of order. For me, It creates the "User" table as "user", and for other members of my team it creates "USER".
I've tried using the #Table annotation (#Table(name="USer")), but it doesn't work.
How do we get EclipseLink to generate consistent table names? Frankly this seems like a rather amateurish mistake for a framework like this.
Sub-question : the reason this is a problem is because EclipseLink by default has no default way of managing schema/data migrations, as far as I know of. The way we're handling it is by writing a bunch of INSERT INTO's to bootstrap the objects we need in our database, and drop-and-recreating the tables every time the schema changes. I know this is not the best practice for propagating schema changes -- does anyone know how this is typically handled in a standard JPA implementation?
Thanks.
By default EclipseLink uses all upper case for the table name, the class User would be USER.
If you specify an #Table annotation with name="USer", then the table will be created as "USer".
Perhaps you are using your own scripts to create the tables, or you database is changing the case based on the OS or its own settings. What database are you using?
If you enable logging in EclipseLink, it will show the exact DDL that it is executing (if it is executing DDL).
In EclipseLink 2.4 there is also a "create-or-extend-tables" DDL generation option to alter existing tables.
We never found any good answer for this. Luckily, we found a workaround for the ways we were using to update the table, which didn't care about capitalization.
As the title says, how do I view the SQL generated by Entity Framework from within my code? I'm running into an error where the EF is crashing because a field is generated by the database (a DateTime field), and I thought I set it to know that the store is generating it via StoreGeneratedPattern, but it's still crashing, so I would like to see what exactly it's trying to push up to the database.
P.S. I've only been using EF for about an hour now... Switching from L2S.
Since you don't have Sql Profiler, your best choice would be LINQPad. You can use your existing assembly.
Click Add connection -> Use a typed data context from your own assembly -> Entity framework and select your dll.
You can write queries directly against your model (or copy-paste from your code). Select the SQL 'tab' under the query window to view the generated SQL code.
You can use the Entity Framework Profiler (EFProf). It's not free, but there's a 30-day trial available. It does a lot more neat stuff besides showing you the SQL statements.
Generally, you should always use SQL Profiler to see the SQL statements that being submitted by EF into your database.
Also, I think you misunderstood about what StoreGeneratedPattern is. If you look at its possible values inside the model, you'll see that it has identity meaning that the value will be generated (by the database) when the row is inserted and will not otherwise change. The other options are Computed, which specifies that the value will be generated on inserts and updates, and None, which is the default.
So EF will not generate that DateTime field on the fly for you, you need to manually create it and then update your model from database so that EF will generate appropriate metadata to work with it at runtime.
The free AnjLab Sql Profiler will work if real SQL Profiler is not available because you're using SQL Server Express: http://anjlab.com/en/projects/opensource/sqlprofiler. It's not quite as nice as the real thing but it gets the job done well enough.
One solution would be to capture the network traffic and have a look at the data on that level. Microsoft Network Monitor does a good job of this.
Of course, that only works if you're using a separate DB server, and the connection is not encrypted.
I have a database that I wish to build an EF model from, however I do not want to include certain columns from the database as the columns concerned are maintained exclusively on the server and should not be manipulated by any application.
Both of the columns are DateTime (if this makes any difference), one of the columns is nullable and is maintained by a trigger on updates and the other is not nullable and set using a default value in the table definition.
I guess I am looking for something like the "Server Generated" option in Linq2Sql; but I cannot find such an option.
Can anybody tell me how to work around this?
Caveat:
I have been trying to introduce business object modelling at my place of work for some years and it has always been rejected because of the amount of additional code that has to be hand-cranked. EF is currently being seen as a viable solution because of the designer and code generation therefore any option that involves hand-cranking the XML will only turn the rest of my colleagues away from EF. I am therefore looking for something that can be done either using the designer or using code.
EDIT:
I guess that what I am looking for here is either...
(a) a way to create the model without EF referencing the columns in the store (ssdl) and therefore not looking to manipulate it in any way
(b) a way to programatically set the "StoreGeneratedPattern" attribute against the property when I create the ObjectContext (the easy answer is to manually manipulate this in the .ssdl, but this would then be overwritten if I refreshed the model from the database and I cannot go down the route where the .csdl, .msl & .ssdl are hand-cranked).
Can you do this with the Entity Framework? Yes; it's easy. Can you do this with the Entity Framework designer? Unfortunately, that is much harder.
The problem you're having is that the column exists in the storage schema (SSDL) in your EDMX. Removing the column with the GUI designer simply removes it from the client schema, not the mapping or the storage schema. However, it's simple enough to go into the EDMX and remove it. Having done that, you can also remove it from the mapping in the client schema portions of the EDMX, and the entity framework will longer complain that it is unmapped.
Problem solved, right?
Well, no. When you use the GUI designer to update the EDMX from the database, the storage schema is thrown away and re-generated. So your column will come back. As far as I know, there is no way to tell the GUI designer to never map a particular column. So you will have to re-do this every time you update with the GUI designer. Fortunately, the EDMX is XML, so you can do this with a XML transform, LINQ, or the XML tool of your choice.
Can you not create a view with the columns you need and import it through entity function wizard and map it to your entities?
You could modify the text template to ignore these columns when generating your entity classes. For example if you added "IGNORE" to the documentation summary, you could modify the template to ignore them by replacing;
Dim simpleProperties as IEnumerable(Of EdmProperty) = typeMapper.GetSimpleProperties(entity)
with;
Dim simpleProperties as IEnumerable(Of EdmProperty) = typeMapper.GetSimpleProperties(entity).Where(Function(p) p.Documentation is nothing orelse p.Documentation.Summary.IndexOf("IGNORE")<0)
Right click on the field in the graphical representation and choose delete. Ive found that sometimes you will get errors when you make a lot of changes to the modeling at once and start to lose track of your changes. Your best bet might be to rebuild the EF generated model.
Keep in mind that when you "update from the database", that old fields on the generated models will not be removed, you will have to remove them manually. For example if you renamed DateField1 to DateField2 in your database, and then you "Update Model from Database", you will now see both DateField1 and DateField2 on the resultant model. This can be a cause of errors.
Do you not want the column to appear in the model at all?
Try selecting the column in the Designer view and hitting the delete key.
Edit
You could make the setter for the property private. Then your app won't be able to modify the value.
Timestamp is a different data type than DateTime. Timestamp seems to be recognized as an attribute the engine manages, much like an identity attribute. You can't "update" a timestamp attribute. Hence, the EDM can manage it correctly (just as it does an identity).
In EDMX designer, select the property and set StoreGeneratedPattern to Computed.