I'm moving from EF Core 2.2 to 3.1. One breaking change (#15392) was that it no longer composed over stored procedures, so you had to add 'AsEnumerable'. That usually works, but I have a stored procedure call on a TPH table where that fails:
My call to the SPROC is:
SqlParameter authorizedUserID_p =
new SqlParameter("#authorizedUserID", authorizedUser.ID);
IEnumerable<Post> query =
context.Posts.FromSqlRaw<Post>("Post.USP_ReadPost #ID, #AuthorizedUserID",
parameters: new[]{ parentID_p, authorizedUserID_p }
).AsEnumerable<Post>();
Post targetPost = query.ToList<Post>().FirstOrDefault<Post>();
And it produces this error, recommending using AsEnumberable (which I'm already using above):
System.InvalidOperationException: FromSqlRaw or FromSqlInterpolated was called with non-composable SQL and with a query composing over it.
Consider calling AsEnumerable after the FromSqlRaw or FromSqlInterpolated method to perform the composition on the client side.
I believe the reason is because my Posts table is Table-per-hiearchy, as other calls to SPROCS in the same application are working fine. Would appreciate any help possible!
This is yet another issue introduced by EFC 3, tracked by #18232: Impossible to use stored procedures related to entities that inherits another one.
The reason is that SP calls are not composable, and EF Core always try to compose SQL for TPH base entities in order to add discriminator condition. Similar to Global Query Filters, but there you can at least use IgnoreQueryFilters, while here you have no option.
The good news is that it's already fixed in EFC repository. The bad news is that it won't be released until EFC 5.0.
Since AsEnumerable() doesn't help, all you can do is to wait for EFC 5.0. Or, if possible, convert SPs like this to TVF (table valued functions) which are composable. In general, use scalar functions or stored procedures with output parameter(s) for non query returning calls (to be executed with ExecuteSql*), and table valued functions for single query returning calls (to be used with FromSql*). Note that currently EFC does not support multiple query returning stored procedures anyway.
Related
I am trying to profile EF to understand more of its inner workings, I have tried to add two entities using the Add method and the AddRange method, then of course committing with the SaveChanges method. And here is what I got on the profiler in both cases.
Does this mean that EF actually makes two trips to the database one per insert? which means that if I am trying to insert 100 entities for example this will mean 100 trips to the database? which will greatly impact performance. or am I missing something here?
Yes, that is correct, it will issue one database call per item attempting to be added, as it is using the standard SQL INSERT command in this case.
The alternatives would be to use BULKINSERT, such as using a stored procedure that takes in an object such as a DataTable.
I need to execute a stored procedure with Entity Framework.
Normally I call it like this:
this.Context.Database.ExecuteSqlCommand("EXEC edi_UploadTransmission");
However, this particular stored procedure includes accessing a linked server.
Since EF wraps ExecuteSqlCommand in a transaction, it is failing, as a linked server is not supported in a transaction (as far as I can tell).
Is there a way to execute this stored procedure with Entity Framework without it being in a transaction?
Pass TransactionalBehavior.DoNotEnsureTransaction as the first parameter to the ExecuteSqlCommand method.
For example,
this.Context.Database.ExecuteSqlCommand(TransactionalBehavior.DoNotEnsureTransaction, "EXEC edi_UploadTransmission");
My recommendation would be to simply not use EF for this part of your code. You can freely combine EF with straight ADO.NET code or with other ORMs such as Dapper or Chain.
https://github.com/docevaad/Chain/wiki/A-Chain-comparison-to-Dapper
I am in the process of converting our internal web application from Linq-To-Sql to EF CodeFirst from an existing database. I have been getting annoyed with Linq-To-Sql's limitations more and more lately, and having to update the edmx after updating a very intertwined database table finally frustrated me enough to switch to EF.
However, I am encountering several situations where using linq with Linq-To-Sql is more powerful than the latest Entity Framework, and I am wondering if anyone knows the reasoning for it? Most of this seems to deal with transformations. For example, the following query works in L2S but not in EF:
var client = (from c in _context.Clients
where c.id == id
select ClientViewModel.ConvertFromEntity(c)).First();
In L2S, this correctly retrieves a client from the database and converts it into a ClientViewModel type, but in EF this exceptions saying that Linq to Entities does not recognize the method (which makes sense as I wrote it.
In order to get this working in EF I have to move the select to after the First() call.
Another example is my query to retrieve a list of clients. In my query I transform it into an anonymous structure to be converted into JSON:
var clients = (from c in _context.Clients
orderby c.name ascending
select new
{
id = c.id,
name = c.name,
versionString = Utils.GetVersionString(c.ProdVersion),
versionName = c.ProdVersion.name,
date = c.prod_deploy_date.ToString()
})
.ToList();
Not only does my Utils.GetVersionString() method cause an unsupported method exception in EF, the c.prod_deploy_date.ToString() causes one too and it's a simple DateTime. Like previously, in order to fix it I had to do my select transformation after ToList().
Edit: Another case I just came across is that EF cannot handle where clauses that compare entities where as L2S has no issues for with it. For example the query
context.TfsWorkItemTags.Where(x => x.TfsWorkItem == TfsWorkItemEntity).ToList()
throws an exception and instead I have to do
context.TfsWorkItemTags.Where(x => x.TfsWorkItem.id == tfsWorkItemEntity.id).ToList()
Edit 2: I wanted to add another issue that I found. Apparently you can't use arrays in EF Linq queries, and this probably annoys me more than anything. So for example, right now I convert an entity that denotes a version into an int[4] and try to query on it. In Linq-to-Sql I used the following query:
return context.ReleaseVersions.Where(x => x.major_version == ver[0] && x.minor_version == ver[1]
&& x.build_version == ver[2] && x.revision_version == ver[3])
.Count() > 0;
This fails with the following exception:
The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities.
Edit 3: I found another instance of EF's bad Linq implementation. The following is a query that works in L2S but doesn't in EF 4.1:
DateTime curDate = DateTime.Now.Date;
var reqs = _context.TestRequests.Where(x => DateTime.Now > (curDate + x.scheduled_time.Value)).ToList();
This throws an ArgumentException with the message DbArithmeticExpression arguments must have a numeric common type.
Why does it seem like they downgraded the ability for Linq queries in EF than in L2S?
Edit (9/2/2012): Updated to reflect .NET 4.5 and added few more missing features
This is not the answer - it cannot be because the only qualified person who can answer your question is probably a product manager from ADO.NET team.
If you check feature set of old datasets then linq-to-sql and then EF you will find that critical features are removed in newer APIs because newer APIs are developed in much shorter times with big effort to deliver new fancy features.
Just list of some critical features available in DataSets but not available in later APIs:
Batch processing
Unique keys
Features available in Linq-to-Sql but not supported in EF (perhaps the list is not fully correct, I haven't used L2S for a long time):
Logging database activity
Lazy loaded properties
Left outer join (DefaultIfEmpty) since the first version (EF has it since EFv4)
Global eager loading definitions
AssociateWith - for example conditions for eager loaded data
Code first since the first version
IMultipleResults supporting stored procedures returning multiple result sets (EF has it in .NET 4.5 but there is no designer support for this feature)
Support for table valued functions (EF has this in .NET 4.5)
And some others
Now we can list features available in EF ObjectContext API (EFv4) and missing in DbContext API (EFv4.1):
Mapping stored procedures
Conditional mapping
Mapping database functions
Defining queries, QueryViews, Model defined functions
ESQL is not available unless you convert DbContext back to ObjectContext
Manipulating state of independent relationships is not possible unless you convert DbContext back to ObjectContext
Using MergeOption.OverwriteChanges and MergeOption.PreserveChanges is not possible unless you convert DbContext back to ObjectContext
And some others
My personal feeling about this is only big sadness. Core features are missing and features existing in previous APIs are removed because ADO.NET team obviously doesn't have enough resources to reimplement them - this makes migration path in many cases almost impossible. The whole situation is even worse because missing features or migration obstacles are not directly listed (I'm afraid even ADO.NET team doesn't know about them until somebody reports them).
Because of that I think that whole idea of DbContext API was management failure. At the moment ADO.NET team must maintain two APIs - DbContext is not mature to replace ObjectContext and it actually can't because it is just a wrapper and because of that ObjectContext cannot die. Resources available for EF development was most probably halved.
There are more problems related. Once we leave ADO.NET team and look on the problem from the perspective of MS product suite we will see so many discrepancies that I sometimes even wonder if there is any global strategy.
Simply live with the fact that EF's provider works in different way and queries which worked in Linq-to-sql don't have to work with EF.
A little late to the game, but I found this post while searching for something else, and figured that I'd post an answer to the fundamental questions in the original post, which mostly boil down to "LINQ to SQL allows Expression [x], but EF doesn't".
The answer is that the query provider (the code that translates your LINQ expression tree into something that actually executes and returns an enumerable set of stuff) is fundamentally different between L2S and EF. To understand why, you have to realize that another fundamental difference between L2S and EF is that L2S is table-based and EF is entity-model-based. In other words, EF works with conceptual entity models, and knows that the underlying physical model (the DB tables) don't necessarily reflect conceptual entities. This is because tables are normalized/denormalized, and have weird ways of dealing with entity type generalization (inheritance). So in EF, you have a picture of the conceptual model (which is the objects you code against in VB/C#, etc.) and a mapping to the physical underlying table(s) that comprise your conceptual entities. L2S does not do this. Every "model entity" in L2S is strictly a single table, with exactly the table fields as-is.
So far, that in and of itself doesn't really explain the problems in the original post, but hopefully, you can begin to appreciate that fundamentally, EF is not L2S+ or L2S v4.0. It's a very different kind of product (a real ORM) even though there is some coincidental overlap in the fact that both use LINQ to get at database data.
One other interesting difference is that EF was built from the ground up to be DB-agnostic, whereas L2S only works against MS SQL Server (although anyone who's sniffed around the L2S code deep enough will see that there are some underpinnings to allow different DBs, but in the end, it was tied to MS SQL Server only). This difference also plays a big role in why some expressions work in L2S LINQ, but not in EF LINQ. EF's query provider deals with canonical DB expressions, which in plain english means LINQ expressions that have SQL query equivalents in nearly all relational databases out there. The underlying EF engine (query provider) translates the LINQ expressions to these canonical DB expressions, then hands the canonical expression tree off to a specific DB provider (say Oracle's or MySQL's EF provider) where it is translated to product-specific SQL. You can see here how these canonical expressions are supposed to be translated by the individual product-specific providers: http://msdn.microsoft.com/en-us/library/ee789836.aspx
Additionally, EF allows some product-specific DB functions (store functions) as expressions through extensions. The underlying product-specific providers are responsible for both providing and translating these.
That being the case, EF only allows expressions that are DB canonical expressions, or store-specific functions, becuase all expressions in the tree are converted to SQL for execution against the DB.
The difference with L2S is that L2S passes off any expressions that it can to the DB from its limited SQL generator, and then executes any expressions it can't translate to SQL on the materialized object set that is returned. While this makes it look simpler to use L2S, what you don't see is that half your expressions don't actually make it to the DB as SQL and this can cause some really inefficient queries bringing back larger sets of data which are then iterated again in CLR memory with regular object LINQ acting against them for the other expressions which L2S can't turn into SQL.
You get the exact same effects in EF by using EF to return the materialized data to object sets in memory, and then using additional LINQ statements on that set in memory - just as L2S does, but in this case, you just have to do it explicitly, just like when you say you have to call .First() before using a non-DB-canonical expression. Similarly, you can call .ToArray() or .ToList() before using additional expressions that can't be turned into SQL.
One other big difference is that in EF, entities must be used whole. Real model entities represent conceptual objects that are transacted on in whole. You never have half a User, for example. The User is an object whose state depends on all fields. If you want to return partial entities, or a flattened join of multiple entities, you have to define a projection (what EF calls a Complex Type), or you can use some of the new 4.1/4.2/4.3 POCO features.
Now that Entity Framework is open source, it's easy enough to see, especially from the comments on Issues from the team, that one of the goals is to provide EF as an open layer on top of multiple databases. To be fair, Microsoft has unsurprisingly only implemented that layer on top of their SQL Server, but there are other implementations, like DevArt's MySql EF Connector.
As part of that goal, it's wise to keep the public interface somewhat limited, and attempting to add an additional layer that asks - well, some of this might be done in memory, some of this might be done in SQL, who knows - definitely complicates the job for other implementers trying to tie EF into this or that database.
So, I agree with the other answer here - you'd have to ask the team - but you can also get a lot of info about that team's direction on the public bug tracker and their other publications, and this seems like a clear motivation.
That said the main difference between LINQ to SQL and EF is the way EF throws an exception on code that has to be run in memory, and if you're an Expressions ninja there's nothing stopping you from going the next step to wrap the DbContext class and make that work just like LINQ to SQL. On the other hand, what you gain there is a mixed bag - you make it implicit rather than explicit when the SQL is generated, and when it fires, and that can be viewed as a loss of performance and control in exchange for flexibility/ease of authoring.
i have a question about the reasonableness of using entity framework only with stored procedures in our scenario.
We plan to have an N-tier architecutre, with UI, BusinessLayer (BLL), DataAccessLayer(DAL) and a BusinessObjectDefinitions(BOD) layer. The BOD layer is known by all other layers and the results from executes queries in the DAL should be transformed into Objects (definied in the BOD) before passing into the BLL.
We will only use stored procedures for all CRUD methods.
So in case of a select stored procedure, we would add a function import, create a complex type and when we execute the function, we tranform the values of the complex type into a class of BOD and pass that to the BLL.
So basicly, we have no Entities in the Model, just Complex types, that are transformed into Business Objects.
I'm not sure if that all makes sense, since in my opinion, we lose a lot of the benefit, EF offers.
Or am i totally wrong?
I would not use EF if all I was just using was stored procs.
Personally, I'd look at something like PetaPoco, Massive or even just straight Ado.Net
EDIT
Here's an example of PetaPoco consuming SPs and outputting custom types
http://weblogs.asp.net/jalpeshpvadgama/archive/2011/06/20/petapoco-with-stored-procedures.aspx
I disagree with both of the existing answers here. Petapoco is great, but I think the EF still offers a number of advantages.
Petapoco works great (maybe even better than the EF) for executing simple stored procedures that read a single entity or a list of entities. However, once you've read the data and need to begin modifying it, I feel this is where the EF is the clear winner.
To insert/update data with petapoco you'll need to manually call the insert/update stored procedure using:
db.Execute("EXEC spName #param1 = 1, #param2 = 2")
Manually constructing the stored procedure call and declaring all the parameters gets old very fast when the insert/update stored procedures insert rows with more than just a couple of columns. This gets even worse when calling update stored procedures that implement optimistic concurrency (i.e. passing in the original values as parameters).
You also run the risk of making a typo in your in-lined stored procedure call, which very likely will not be caught until runtime.
Now compare this to the entity framework: In the EF I would simply map my stored procedure to my entity in the edmx. There's less risk of a typo, since the entity framework tools will automatically generate the mapping by analyzing my stored procedure.
The entity framework also will handle optimistic concurrency without any problems. Finally, when it comes time to save my changes the only step is to call:
entities.SaveChanges()
I agree, if you rely on stored procedures for all CRUD methods, then there is no need to use EF.
I use EF to map stored procedure calls as our DAL. It saves time in writing your DAL by mapping the functions. We are not using LINQ to SQL as much, as our DBA does not want direct data table access.
So it turns out that I am the last person to discover the fundamental floor that exists in Microsoft's Entity Framework when implementing TPT (Table Per Type) inheritance.
Having built a prototype with 3 sub classes, the base table/class consisting of 20+ columns and the child tables consisting of ~10 columns, everything worked beautifully and I continued to work on the rest of the application having proved the concept. Now the time has come to add the other 20 sub types and OMG, I've just started looking the SQL being generated on a simple select, even though I'm only interested in accessing the fields on the base class.
This page has a wonderful description of the problem.
Has anyone gone into production using TPT and EF, are there any workarounds that will mean that I won't have to:
a) Convert the schema to TPH (which goes against everything I try to achieve with my DB design - urrrgghh!)?
b) rewrite with another ORM?
The way I see it, I should be able to add a reference to a Stored Procedure from within EF (probably using EFExtensions) that has the the TSQL that selects only the fields I need, even using the code generated by EF for the monster UNION/JOIN inside the SP would prevent the SQL being generated every time a call is made - not something I would intend to do, but you get the idea.
The killer I've found, is that when I'm selecting a list of entities linked to the base table (but the entity I'm selecting is not a subclass table), and I want to filter by the pk of the Base table, and I do .Include("BaseClassTableName") to allow me to filter using x=>x.BaseClass.PK == 1 and access other properties, it performs the mother SQL generation here too.
I can't use EF4 as I'm limited to the .net 2.0 runtimes with 3.5 SP1 installed.
Has anyone got any experience of getting out of this mess?
This seems a bit confused. You're talking about TPH, but when you say:
The way I see it, I should be able to add a reference to a Stored Procedure from within EF (probably using EFExtensions) that has the the TSQL that selects only the fields I need, even using the code generated by EF for the monster UNION/JOIN inside the SP would prevent the SQL being generated every time a call is made - not something I would intend to do, but you get the idea.
Well, that's Table per Concrete Class mapping (using a proc rather than a table, but still, the mapping is TPC...). The EF supports TPC, but the designer doesn't. You can do it in code-first if you get the CTP.
Your preferred solution of using a proc will cause performance problems if you restrict queries, like this:
var q = from c in Context.SomeChild
where c.SomeAssociation.Foo == foo
select c;
The DB optimizer can't see through the proc implementation, so you get a full scan of the results.
So before you tell yourself that this will fix your results, double-check that assumption.
Note that you can always specify custom SQL for any mapping strategy with ObjectContext.ExecuteStoreQuery.
However, before you do any of this, consider that, as RPM1984 points out, your design seems to overuse inheritance. I like this quote from NHibernate in Action
[A]sk yourself whether it might be better to remodel inheritance as delegation in the object model. Complex inheritance is often best avoided for all sorts of reasons unrelated to persistence or ORM. [Your ORM] acts as a buffer between the object and relational models, but that doesn't mean you can completely ignore persistence concerns when designing your object model.
We've hit this same problem and are considering porting our DAL from EF4 to LLBLGen because of this.
In the meantime, we've used compiled queries to alleviate some of the pain:
Compiled Queries (LINQ to Entities)
This strategy doesn't prevent the mammoth queries, but the time it takes to generate the query (which can be huge) is only done once.
You'll can use compiled queries with Includes() as such:
static readonly Func<AdventureWorksEntities, int, Subcomponent> subcomponentWithDetailsCompiledQuery = CompiledQuery.Compile<AdventureWorksEntities, int, Subcomponent>(
(ctx, id) => ctx.Subcomponents
.Include("SubcomponentType")
.Include("A.B.C.D")
.FirstOrDefault(s => s.Id == id));
public Subcomponent GetSubcomponentWithDetails(int id)
{
return subcomponentWithDetailsCompiledQuery.Invoke(ObjectContext, id);
}