Can anyone help me, to convert the below sql query to Linq (Lambda Expressions).
Thanks in Advance.
SQL Query:
UPDATE A INNER JOIN B ON (A.Trade Number=B.Trade Number) AND
(A.AccountId=B.AccountId) SET A.Float = B.CCY, A.Float = B.BASIS,
A.LastReset = B.FIXING, A.LastLibor = B.INTRATE;
Updates are not expressed as LINQ statements. You can use LINQ to load the record you wish to modify, but the actual update will involve a separate method call, the details of which will depend on which database technology you're using.
So, assuming you already have a reference to the record you wish to update from A, load the associated record from B (using LINQ), perform the updates to A programatically, and then save the changes to A.
Here's an example using LINQ-to-SQL.
Related
I am trying to create an SAP data query using SQVI (or SQ01) to display all entries that meet certain criteria. I can use the 'Selection Fields' tab to have a user specify any of these parameters, but I want to be able to query the data with more complex conditions such as a nested 'AND'/'OR'. I have researched the question for a couple hours and have yet to find a solution that works. Here is an example simplified query that I would like to do, written in SQL form:
SELECT t0.name, t0.birthYear, t1.grade, t1.county
FROM t0
INNER JOIN t1 on t0.personID = t1.personID
WHERE t0.name = 'Bob'
AND t0.birthyear = 2000
AND (t1.grade = 12
OR t1.county <> 'Cook');
Now the tricky part is figuring out how to do a nested 'AND' and 'OR' in SQVI. At first, I pulled all the data without these conditions, exported it to Excel, and then performed this logic to get the correct entries that meet these criteria. However, I do not want to do this every time, as it is highly repetitive and there HAS TO be some solution within the SAP environment. Ideally, I would be able to create a query that I can share with co-workers to execute once a week, where they don't need to enter any values to test against 'name', 'birthyear', 'grade', or 'county'. They should be able to type in the code for this query and hit execute, and it should spit out all of the entries that meet all the criteria. I want to be able to hard-code the testing parameters in this instance.
Let me know if this is even possible! If it's not possible using SQVI, what would I need access to in order to do a complex conditional query like this? I do not have write-access on the data, so I am not authorized to use 'DBACOCKPIT' to write the query as SQL (which would be so much simpler).
I'm using EF core 2 as ORM in my project.
I faced this problem while executing this query:
var query = (from droitsGeo in _entities.DroitsGeos
join building in _entities.Batiments
on droitsGeo.IdPerimetre equals building.IdBatiment
where droitsGeo.IdUtilisateur == idUser &&
droitsGeo.IdClient == idClient &&
building.Valide == true &&
droitsGeo.IdNiveauPerimetre == geographicalLevel
orderby sort ascending
select new GeographicalModel
{
Id = building.IdBatiment,
IdParent = building.IdEtablissement,
Label = building.LibBatiment,
});
First execution tooks about 5 second and second less than one second as show below :
First execution of query :
Time elapsed EF: 00:00:04.8562419
After first execution of query :
Time elapsed EF: 00:00:00.5496862
Time elapsed EF: 00:00:00.6658079
Time elapsed EF: 00:00:00.6176030
I have same result using Stored procedure.
When i execute sql query generated by EF in SQL Server, the result is returned in less than a second.
what is wrong with EF Core 2 or did i miss something in configuration?
The EF by default tracks all the entities you run queries against.
When you run it for the first time the track change mechanism kicks in... that's why it takes a little bit longer.
You can avoid this, especially when retrieving collections by using .AsNoTracking() when composing the query.
Take a look:
var items = DbContext.MyDbSet
.Include(SecondObject)
.AsNoTracking()
.ToList();
EF core needs to compile LINQ quires using reflection therefor first queries are always slow. There is already a GitHub issue here
I have a simple idea to resolve this issue with the help of stored procedures and thereafter AutoMapper.
Create an stored procedures that return all the columns that you want, no matter if they are from different tables. Once the data is received from the stored procedure and you have received the object in one of your Model classes, you can then use AutoMapper to map only the relevant attributes to other classes. Please note that I am not giving you a tutorial of how to use stored procedure. I am giving you an example that might explain better:
A stored procedure is created which returns results from three tables named A, B and C.
A model class named SP_Result.cs is created corresponding to created stored procedure to map the received object of stored procedure (this is required when working with stored procedures in EF Core)
'ViewModels` are created having same attributes as returning from each table A, B and C.
Thereafter, mapping configurations will be created for SP_Result with ViewModel of Class A, Class B and Class C. e.g. CreateMap<SP_Result, ViewModel_A>(); CreateMap<SP_Result, ViewModel_B>();. I suppose, you would have a request and response objects which can be used instead of ViewModels. Name the properties accordingly in the stored procedure using AS keyword. e.g. Select std_Name AS 'Name'
This mapping will map the individual properties to each class. AutoMapper ignore the properties which do not exists in either of the classes mentioned in Mapping Configuration.
If you are selecting a list of objects where each object does have its own list of objects, this scenario will generally create N + 1 queries in EF. In fact, if you try to achieve this using stored procedures, you will have to create multiple queries or run the stored procedure multiple times (in a loop may be), or you will end up receiving Cartesian product.
suppose my LINQ query is like
var qry = from c in nwEntitiesContext.CategorySet.AsEnumerable()
let products = this.GetProducts().WithCategoryID(c.CategoryID)
select new Model.Category
{
ID = c.CategoryID,
Name = c.CategoryName,
Products = new Model.LazyList<Core.Model.Product>(products)
};
return qry.AsQueryable();
i just want to know what query it will generate at runtime....how to see what query it is generating from VS2010 IDE when we run the code in debug mode....guide me step by step.
There is not much to see here - it will just select all fields from the Category table since you call AsEnumerable thus fetching all the data from the Category table into memory. After that you are in object space. Well, depending on what this.GetProducts() does - and my guess it makes another EF query fetching the results into memory. If that's the case, I would strongly recommend you to post another question with this code and the code of your GetProducts method so that we can take a look and rewrite this in a more optimal way. (Apart from this, you are projecting onto a mapped entity Model.Category which again won't (and should not) work with Linq-to-Entities.)
Before reading into your query I was going to recommend doing something like this:
string sqlQueryString = ((ObjectQuery)qry).ToTraceString();
But that won't work since you are mixing Linq-to-Entities with Linq-to-objects and you will actually have several queries executed in case GetProducts queries EF. You can separate the part with your EF query and see the SQL like this though:
string sqlString = nwEntitiesContext.CategorySet.ToTraceString();
but as I mentioned earlier - that would just select everything from the Categories table.
In your case (unless you rewrite your code in a drastic way), you actually want to see what queries are run against the DB when you execute the code and enumerate the results of the queries. See this question:
exact sql query executed by Entity Framework
Your choices are SQL Server Profiler and Entity Framework Profiler. You can also try out LinqPad, but in general I still recommend you to describe what your queries are doing in more detail (and most probably rewrite them in a more optimal way before proceeding).
Try Linqpad
This will produce SELECT * FROM Categories. Nothing more. Once you call AsEnumerable you are in Linq-to-objects and there is no way to get back to Linq-to-entities (AsQueryable doesn't do that).
If you want to see what query is generated use SQL Profiler or any method described in this article.
I have a List and each Filter object has a property called "Id". I want to fetch all the records from my database using Linq to SQL that contains those ids. The List is not part of the database it is just an independent list.
not very clear question. however this is what, i suppose, u r trying to do
from c in datacontext.TableName where
IndependentList.Contains(c=>c.id)
select c
So I'm extremely new to Linq in .Net 3.5 and have a question. I use to use a custom class that would handle the following results from a store procedure:
Set 1: ID Name Age
Set 2: ID Address City
Set 3: ID Product Price
With my custom class, I would have received back from the database a single DataSet with 3 DataTables inside of it with columns based on what was returned from the DB.
My question is how to I achive this with LINQ? I'm going to need to hit the database 1 time and return multiple sets with different types of data in it.
Also, how would I use LINQ to return a dynamic amount of sets depending on the parameters (could get 1 set back, could get N amount back)?
I've looked at this article, but didn't find anything explaining multiple sets (just a single set that could be dynamic or a single scalar value and a single set).
Any articles/comments will help.
Thanks
I believe this is what you're looking for
Linq to SQL Stored Procedures with Multiple Results - IMultipleResults
I'm not very familiar with LINQ myself but here is MSDN's site on LINQ Samples that might be able to help you out.
EDIT: I apologize, I somehow missed the title where you mentioned you wanted help using LINQ with Stored Procedures, my below answer does not address that at all and unfortunately I haven't had the need to use sprocs with LINQ so I'm unsure if my below answer will help.
LINQ to SQL is able hydrate multiple sets of data into a object graph while hitting the database once. However, I don't think LINQ is going to achieve what you ultimately want -- which as far as I can tell is a completely dynamic set of data that is defined outside of the query itself. Perhaps I am misunderstanding the question, maybe it would help if you provide some sample code that your existing application is using?
Here is a quick example of how I could hydrate a anonymous type with a single database call, maybe it will help:
var query = from p in db.Products
select new
{
Product = p,
NumberOfOrders = p.Orders.Count(),
LastOrderDate = p.Orders.OrderByDescending().Take(1).Select(o => o.OrderDate),
Orders = p.Orders
};