I have created a view on SQL Server which produces a report for monthly totals. The view has been added to my DB Context and mapped successfully, therefore I am in a position where I can successfully get the results of my view as follows:
var list = db.MonthlyTotals.ToList();
However, I need to be able to restrict between dates and therefore needs to pass in some parameters for a start and end date.
Is this possible with either EF Core 6 or 7? Or do I need to use stored procedures instead?
I have created a view...I need to be able to restrict between dates and therefore needs to pass in some parameters for a start and end date...Is this possible with either EF Core 6 or 7?
Views don't use parameters, that's by design of the SQL Server Engine, and has nothing to do with whatever ORM you use, such as EF Core. If you really want to use parameters, then use stored procedures.
But the good news is, your use case is simple enough that you shouldn't need parameters anyway. Like Gert suggested in the comments, just use a Where clause against your view instead.
You can achieve this in C# with LINQ's method syntax like so:
var list = db.MonthlyTotals
.Where(mt => mt.YourDateColumn >= someDateVariable && my.YourDateColumn < someOtherDateVariable)
.ToList();
There's also query syntax with LINQ, which more closely resembles T-SQL code, but in my opinion is less intuitive in the context of C# as opposed to method syntax.
Related
I have this query to be executed :
Select * From Products WHERE Title like '%search text%'
ORDER BY Difference(Title, 'search text') DESC
Now I want to implement the above query using EntityFrameworkCore and linq.
So how can I call difference function to order products by closest match in Title column?
Every IQueryable holds an Expression and a Provider. The Expression holds the query that must be performed. The Provider knows who has to execute the query, usually a database management system. It is the task of the Provider to translate the Expression into the language that the database understands (something SQL-like) and to execute the query. The Provider will fetch the results in an efficient way and return the queried data as an enumerable object.
The IQueryable implements IEnumerable.
When you use LINQ functions like ToList(), FirstOrDefault(), Any(), or use the query in a foreach, then internally IEnumerable.GetEnumerator() is called and Enumerator.MoveNext()
This will order the Provider to translate the Expression into SQL and execute the query. The returned enumerable is used to enumerate over the returned items.
It is the task of the programmer of the class that implements the IQueryable to implement the translation of the Expression into SQL. This is not easy, and I think the people who created entity framework did a great job.
However, some items known in SQL are very difficult to implement. Among those are the notions of SoundEx and Difference. I'm not sure, but I think that one of the reasons that made this difficult is that they are typically something used in SQL, and not in any other kind of IQueryable systems.
In fact, there are a several functions that are not supported by entity framework. See Supported and unsupported LINQ methods (LINQ to entities).
Your DbContext is an abstract representation of your database model. Users of it should not care whether it uses Microsoft SQL, MySQL, or whether it is a data collection that doesn't use anything similar to SQL.
But if you are absolutely certain that it is okay to limit your DbContext to only a certain kind of databases, one that knows the concepts of SoundEx and Difference, consider creating a stored procedure for your query. See How to call a Stored Procedure in Entity Framework
SQL can not understand the Difference function written in c#. To make it work you will have to fetch values from Products table in a c# collection like List
Then do ordering on that list using Difference function
We have about 2'000 "old" objects in a sql server database (tables, views etc.) of which we don't really know if they're still in use. I want to create an extended event listener for these objects. I tried to add a giant WHERE clause to the CREATE EVENT SESSION command, consisting of 2'000 [package0].[equal_int64]([object_id], (<objectId>)) statements.
However, the command max length is 3'000 characters, so I cannot do this. And I guess that the performance of this filer wouldn't be too good, anyway...
Now my question is: I can query all possible predicates using select * from sys.dm_xe_objects where object_type= 'pred_compare'. this gives me results such as name=equal_uint64, package_guid=60AA9FBF-673B-4553-B7ED-71DCA7F5E972. the package_guid refers to sys.dm_xe_packages, where several DLLs are referenced which seem to implement a particular predicate.
Would it be possible to define my own "package" and implement a predicate there (which would filter the objectId using a hashtable)? Is it possible somehow to import such a package into SQL server so I could define a custom predicate?
Or does anyone have another idea how to implement such a filter?
I am new to SQL Server and I would like to know how to return the exact columns of tables in UDFs.
The situation is like this : I am going to query a table and then return it again as table.
Example :
create function test
var t
set t = select * from table where condition
return t;
How am I going to do it?
(question is only how to return the table with dynamic fields)
Hope you understand the question. Thanks in advance
UPDATE : my question is somehow like how do I create a table variable where its columns are dynamic.
User defined functions have several limitations (they are meant not to have side-effects - cannot anything in the database - etc.). For your particular case, the following prohibit you to do your work:
dynamic SQL cannot be used
temporary tables are not allowed
So, a function can only work if it knows what is the structure of the result at compile time.
I would consider a procedure to achieve what you need, since it allows more flexibility. However, this comes with the headache of sharing data between stored procedures.
It is not specified in the question, but ideally, this dynamic processing should stay in a high level language like C# or Java that have more support for dynamic structures (e.g. LINQ or Dynamic LINQ in C#)
I am trying to fetch the current timestamp through a stored procedure in HQL. This means my code looks something like the following:
var currentTimestamp =
session.CreateQuery("SELECT CURRENT_TIMESTAMP()")
.UniqueResult<DateTime>();
This doesn't work. Specifically, it throws a System.NullReferenceException deep inside of the NHibernate HqlParser.cs file. I played around with this a bit, and got the following to work instead:
var currentTimestamp =
session.CreateQuery("SELECT CURRENT_TIMESTAMP() FROM Contact")
.SetMaxResults(1)
.UniqueResult<DateTime>();
Now I have the data I want, but an HQL query I don't. I want the query to represent the question I'm asking -- like my original format.
An obvious question here is "Why are you using HQL?" I know I can easily do with this session.CreateSQLQuery(...), hitting our MySQL 5.1 database directly. This is simply an example of my core problem, with the root being that I'm using custom parameter-less HQL functions throughout my code base, and I want to have integration tests that run these HQL parameter-less functions in as much isolation as possible.
My hack also has some serious assumptions baked in. It will not return a result, for example, if there are no records in the Contact table, or if the Contact table ceases to exist.
The method to retrieve CURRENT_TIMESTAMP() (or any other database function) outside of the context of a database table varies from database to database - some allow it, some do not. Oracle, for example, does not allow a select without a table, so they provide a system table with a single row which is called DUAL.
I suspect that NHibernate is implementing in HQL primarily features which are common across all database implementations, and thus does not implement a table-less select.
I can suggest three approaches:
Create a view that hides the table-less select such as 'create view dtm as select current_timestamp() as datetime'
Follow the Oracle approach and create a utility table with a single row in it that you can use as the table in a select
Create a simple stored procedure which only executes 'select current_timestamp()'
When using multivalue parameters in sql reporting services is it more appropriate to implement the list filter using a filter on the dataset itself, the data region control or change the actual query that drives the dataset?
SSRS will support any scenario, so then I ask, is there a reason beyond the obvious of why this should be done at one level over another?
It makes sense to me that modifying the query itself and asking the RDBMS to handle the filtering would be most efficient but maybe I am missing something with respect to how the SSRS Data Processing Extension may handle this scenario?
You are correct. The way to go is to pass the parameters through to the database engine.
Reporting Services should only be ideally used to render content. The less data that you need to pass back to the client web browser, the faster the report will render.
You may find my answer to a similar post regarding using mulit-value parameters to be of use.
Passing multiple values for a single parameter in Reporting Services
Hope this helps but please feel free to pose any further questions you may have.
Cheers,
John
Using table-valued UDF is a good approach, but there is still one issue - in case if this function is called in many places of query, and even inside inner select, there can be performance problem. You can resolve this issue using table variable (or temp table eather):
DECLARE #Param (Value INT)
INSERT INTO #Param (Value)
SELECT Param FROM dbo.fn_MVParam(#sParameterString,',')
...
where someColumn IN(SELECT Value FROM #Param)
so function will be called only once.
Othe thing, if you don't use stored procedure, but embedded SQL query instead, you can just put MVP into query:
...
where someColumn IN(#Param)
...
Use the RDBMS to do the main filtering
SSRS provides filtering for the purposes on data driven display and/or dynamic display. Especially useful for sub reports etc