With EF4, is it possible to get the generated SQL for Updates/Inserts rather than executing it... just like you can view the query SQL before it runs.
The reason is, I have a set of helper functions that execute SQL commands. For instance...
Decrement<Category>("ProductCount", categoryID);
SetNull<Product>("CategoryID", productID);
Which generates...
UPDATE Categories
SET ProductCount = ProductCount - 1
WHERE CategoryID = #CategoryID;
UPDATE Products
SET CategoryID = NULL
WHERE CategoryID = #ProductID;
I usually run several commands per operation, so with each helper function call, the SQL is generated and stored. When I call SaveChanges(), all of the commands are run at ONE time.
The only problem is that EF runs its commands separately behind the scenes, then I run the others right afterward. It would be ideal to run everything as one single command.
You can get it at design time with Sql Profiler, but I think you're meaning that you want it at run-time. Here's an example I found on how to do that:
public static void WriteGeneratedSql(EntityCommand cmd)
{
cmd.Prepare();
IServiceProvider isp = (IServiceProvider)EntityProviderFactory.Instance;
DbProviderServices mps = (DbProviderServices)isp.GetService(typeof(DbProviderServices));
EntityCommandDefinition definition = (EntityCommandDefinition)mps.CreateCommandDefinition(cmd);
int commandId = 1;
foreach (string commandText in definition.MappedCommands)
{
Console.WriteLine("Generated Command {0}:", commandId);
commandId++;
Console.WriteLine(commandText);
}
}
Found here.
Related
Is it possible to invoke a user-defined SQL function from the query interface in EF Core? For example, the generated SQL would look like
select * from X where dbo.fnCheckThis(X.a, X.B) = 1
In my case, this clause is in addition to other Query() method calls so FromSQL() is not an option.
I just managed this with help from this article (H/T #IvanStoev for his comment on the question).
In your DbContext class:
[DbFunction("my_user_function_name")]
public static bool SatisfiesMyUserFunction(int i)
{
throw new Exception(); // this code doesn't get executed; the call is passed through to the database function
}
Note that the function must be in the DbContext class, even though it is static.
Then create a database migration and define the user function in the script.
Usage:
var query = db.Foos.Where(f => MyDbContext.SatisfiesMyUserFunction(f.FieldValue));
I'm writing a driver for EF Core for Spanner - In basic level it works and I can write Read and Write Queries that get's translated to Spanner SQL , executed and return results etc..
Now I'm trying to add Support For Read Query with Secondary Index.
Ultimately I'm trying to generate this SQL Query:
SELECT * FROM PostTags#{ FORCE_INDEX = PostTagsByTagId } WHERE TagId = 1
From This Linq:
var postTag = ctx.PostTags.WithIndex("PostTagsByTagId").Where(x => x.TagId == 1).FirstOrDefault();
I've added extension method as follow:
public static class SpannerIndexSupport
{
public static IQueryable<TSource> WithIndex<TSource>(this IQueryable<TSource> query, string indexName)
{
var methodDefinition = typeof(SpannerIndexSupport).GetTypeInfo().GetMethods().Single(m => m.Name == "WithIndex");
var method = methodDefinition.MakeGenericMethod(typeof(TSource));
var args = new[] { query.Expression, Expression.Constant(indexName) };
var expression = Expression.Call(null, method, args);
return query.Provider.CreateQuery<TSource>(expression);
}
}
And tried to write IAsyncQueryProvider to support it but couldn't find a way to make it work.
Any ideas Anyone?
In the official Spanner EFCore library (https://github.com/GoogleCloudPlatform/google-cloud-dotnet/tree/master/apis/Google.Cloud.EntityFrameworkCore.Spanner/Google.Cloud.EntityFrameworkCore.Spanner), I would start by overriding VisitTable(TableExpression tableExpression) in SpannerQuerySqlGenerator:
https://github.com/GoogleCloudPlatform/google-cloud-dotnet/tree/master/apis/Google.Cloud.EntityFrameworkCore.Spanner/Google.Cloud.EntityFrameworkCore.Spanner/Query/Sql/Internal/SpannerQuerySqlGenerator.cs
This will allow you to get a proof of concept going because you can directly influence the generated SQL text there.
Once that works, then you will want to make it proper.
I suppose there might be a few ways to make this work. The simplest might be to have some custom no-op method marker in the Linq expression tree and then register an IMethodCallTranslator to convert it either to a custom spanner specific Expression (whose Accept calls into SqlGenerator to generate the proper Sql) or possibly creating a SqlTranslatingExpressionVisitor to switch out the table expression to a custom one that allows the FORCE_INDEX.
Sorry I couldn't help more.
This is now supported in the official Entity Framework provider for Google Cloud Spanner. You can add this by adding a tag to the query like this:
var singersOrderedByFullName = context.Singers
// This will add the following comment to the generated query:
// `-- Use hint: force_index FullName`
// This comment will be picked up by the interceptor and an index
// hint will be added to the query that is executed.
.TagWith("Use hint: force_index FullName")
.OrderBy(s => s.FullName)
.AsAsyncEnumerable();
A full example can be found here: https://github.com/googleapis/dotnet-spanner-entity-framework/blob/main/Google.Cloud.EntityFrameworkCore.Spanner.Samples/Snippets/QueryHintSample.cs
I am trying to get an entity with EF by having an initial sql as input.
I tried the context.Entities.SQLQuery method but this returns a DBSet when I require an IQueriable.
I learned that I cannot transform DBSet to IQueryable because the first is already a result of data while the second is the container for the results of a "query" (executed yet or not). Correct me if i'm wrong :)
So I thought that when I write the following lambda I get the resulting query:
db.MyTable.Where(x => x.id == "123")
Becomes:
SELECT * FROM myTable WHERE id = '123'
With this I thought if I can set directly my query without needing to set my lambda...
Is that an option?
Or an alternative?
Thanks!
It's a bit unclear what you mean:
I am trying to get an entity with EF having an initial sql as input.
I'd interpret this, as that you have an SQL statement as input of something and you want to get an entity framework entity that would have this statement (whatever having a statement means)? Not understandable!
I learned that I cannot transform DBSet to IQueryable because the
first (the DbSet) is already a result of data while the second (the IQueryable) is the container for the results of a "query"
NOT!
Every DbSet<T> implements IQueryable<T>, meaning that if you have an object of class DbSet<t>, this object implements all functionality of IQueryable<T>. Just using this IQueryable does not execute the query. The query will only be executed once the first element of the sequence if requested.
using (var dbContext = new MyDbcontext())
{
var result = dbContext.MyItems
.Where(item => ...)
.Select(item => new
{
X = item.Property1,
Y = item.Property2,
...
};
Until here, the first element of the sequence is not asked, the query is not performed yet. No communication with the database was needed (except to create the dbContext object)
Only if you use execution functions like ToList(),Count(), First(), Max(), etc, the query is performed.
You can check this, because you get exceptoin if you do these kind of functions after the using block:
Wrong
IQueryable largeItems;
using (var dbContext = new MyDbcontext())
{
largeItems = dbContext.MyItems
.Where(item => item.Size > 1000);
// query not executed yet
}
int nrOfLargeItems = largeItems.Count();
// exception, query executed after dbContext is disposed
correct
int nrOfLargeItems;
using (var dbContext = new MyDbcontext())
{
var largeItems = dbContext.MyItems
.Where(item => item.Size > 1000);
// query not executed yet
nrOfLargeItems = largeItems.Count();
// the query is performed
}
Conclusion: users of a DbSet<T> inside a dbContext can use the DbSet<T> as if it was an IQueryable<T>, the query will not be executed until you perform any function that needs the first element of the query.
This includes complex functions like Join, GroupBy, OrderBy, etc. You can recognize these functions because MSDN add the following to the remarks section
This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach.
I'm currently planning on switching my "manual query-writing" code to a nice SQL framework, so I can leave the queries or sql things to the framework, instead of writing the queries myself.
Now I'm wondering how I can get a single record from my table in Entity Framework 4?
I've primarily used SQL like SELECT * FROM {0} WHERE Id = {1}. That doesn't work in EF4, as far as I'm concerned.
Is there a way I can select a single ID-Based record from my Context?
Something like:
public Address GetAddress(int addressId)
{
var result = from Context.Addresses where Address.Id = addressId;
Address adr = result as Address;
return Address;
}
Thank you!
var address = Context.Addresses.First(a => a.Id == addressId);
You can use Single or First methods.
The difference between those methods is that Single expects a single row and throws an exception if it doesn't have a single row.
The usage is the same for both of them
(Based on VS 2015) If you create an .edmx (Add --> ADO.NET Entity Data Model).
Go through the steps to created the ".edmx" and use the following to run the stored procedure. emailAddress is the parameter you are passing to the stored procedure g_getLoginStatus. This will pull the first row into LoginStatus and status is a column in the database:
bool verasity = false;
DBNameEntities db = new DBNameEntities(); // Use name of your DBEntities
var LoginStatus = db.g_getLoginStatus(emailAddress).FirstOrDefault();
if ((LoginStatus != null) && (LoginStatus.status == 1))
{
verasity = true;
}
I'm having problems querying the entity model to get additional information.
My db has a Program table with a one to many relation with an Events table. The Entity model generates the relationships just fine, but I'm unable to figure out how to query the model to get the progam object with its events.
I can do this:
var foo = from program in entities.ProgramSet
where program.StartDate > DateTime.now
orderby program.StartDate
select program;
No problems there. From what I've found on Microsofts Page (Shaping queries with Entity framework): msdn.microsoft.com/en-us/library/bb896272.aspx, if I wanted to get the child objects, I just do the following:
// Define a LINQ query with a path that returns
// orders and items for a contact.
var contacts = (from contact in context.Contact
.Include("SalesOrderHeader.SalesOrderDetail")
select contact).FirstOrDefault();
However, there is no .Include or Include that I can find on the query.
Any suggestion? I know that I can do a foreach across the results, then run a .Events.Load() on it, but doesn't that force the IQueriable result to execute the sql, instead of optomize it to run only when a .ToList() etc is called on it?
Here is some sample code from my project:
public class ProgramRepository : CT.Models.IProgramRepository
{
CTEntities db = new CTEntities();
public IQueryable<Program> FindAllPrograms()
{
return db.ProgramSet;
}
public IQueryable<Program> FindUpcomingPrograms()
{
var programs = from program in FindAllPrograms()
where program.StartDate > DateTime.Now
orderby program.StartDate
select program;
return programs;
}
With the FindUpComingPrograms I would like to have it also include the Events Data. There is a relationship between the Program and Events model. Program has a List<Events> property, that I would like to fill and return with the IQueryable method.
Thanks again!
The Include Function is part of the ObjectQuery object...
I think you are going to need to re-write your query to look something like this:
var contacts = context.Contact.Include("SalesOrderHeader.SalesOrderDetail").FirstOrDefault();
//Not sure on your dot path you might have to debug that a bit
Here is an Article that has some examples...