Can someone convert the following simple SQL statement into LINQ? The StudentID is of type int.
select * from Student where studentId like '%1001%';
Thank you!
ctx.Student.Where(x => x.StudentId.Contains("1001"))
It's strange that you have an ID of string type.
Use int instead.
O, sorry, I see now, you wrote that ids are ints. In that case you cannot use like in SQL.
It doesnt make sense. You must convert int to string first.
ctx.Student.Where(x => x.StudentId.ToString().Contains("1001"))
Try this:
db.Students.Where(s => s.StudentID.ToString().Contains("1001"))
Use the Contains operator:
from s in Student
where s.studentId.ToString().Contains("1001")
select s;
Related
I'm hoping this is a simple solution. I have a field (PressType) in a table (Stocks) that is seed populated by using an Enum. The table stores the data as an integer. However when I want to query some data via Linq it gives me issues. I can filter any other fields in the table using this format however on the Enum populated field it says
the "==" operator cannot be applied to operands of type "Models.PressType" and "string".
Any help you could give would be appreciated, thanks.
var test = db.Stocks.Where(x => x.PressType == myValue);
There is nothing wrong with your Linq. Your problem is that myValue is of type string. You need to convert your string to the enum first.
string myValue = SomeControl.Text;
Models.PressType myValueAsEnum = (Models.PressType)
Enum.Parse(typeof(Models.PressType), myValue);
IQueryable<Stock> test = db.Stocks.Where(x => x.PressType == myValueAsEnum);
I got a Entity with a Integer
#Entity(name=customer)
public Customer {
...
#Column
private int number;
...
//getter,setter
}
Now I want to cast this Integer in a query to compare it with an other value.
I tried this Query:
"SELECT c FROM customer c WHERE CAST(c.number AS TEXT) LIKE '1%'"
But it doesn't work.
This works in some of my code using Hibernate:
SELECT c FROM customer c WHERE STR(c.number) LIKE '1%'
In general, this is what the Hibernate docs (14.10 Expressions) say on casting:
str() for converting numeric or temporal values to a readable string
cast(... as ...), where the second argument is the name of a Hibernate
type, and extract(... from ...) if ANSI cast() and extract() is
supported by the underlying database
Since EJB3 EJBQL has been (almost) replaced by JPQL. In EJBQL and according to http://docs.oracle.com/cd/E11035_01/kodo41/full/html/ejb3_langref.html in JPQL as well there is no functionality to CAST a property of an entity.
So like I already told there are two options left:
Use a native Query.
Add special cast methods to the entities.
You need to specify the column you're selecting from table alias c, and since EJBQL doesn't support a cast function, pass a string into the query instead of text. (This effectively allows your program to do the cast before it gets to EJBQL.)
The example below is in SQL Server, but should give you the idea:
declare #numberText as varchar(50)
set #numberText = '1'
SELECT c.CustomerNumber FROM customer c
WHERE c.CustomerNumber LIKE #numbertext + '%'
So instead of private int number use private string numberText.
NOTE: I edited this answer after OP confirmed EJBQL does not support a CAST function.
I have a column that's defined as an integer in EF (Code First). I want to search it using "starts with." Now, I can do this:
Where(x => SqlFunctions.StringConvert((double)x.AccountNumber).StartsWith(searchTerm))
However, SqlFunctions.StringConvert() gets translated to the T-SQL function STR(), which left-pads the result for reasons which are beyond my comprehension.
Also, I can't use string.TrimStart() because it's not supported by the Entity Framework.
Can anyone lend any help?
Trim() and TrimStart() work in LINQ to Entities, so you can use:
Where(x => SqlFunctions.StringConvert((double)x.AccountNumber)
.TrimStart().StartsWith(searchTerm))
TrimStart translates into LTRIM in SQL. With searchTerm = 123 for example you get something like:
WHERE LTRIM(STR( CAST( [Extent1].[AccountNumber] AS float))) LIKE N'123%'
In SQL I do it like this:
DateMonth=convert(datetime, convert(char(6), AASI.Inv_Acctcur) + '01')
How to do it in LINQ? String is in following format:
"yyyyMMdd"
Thanks,
Ile
EDIT:
Example of SQL usage:
SELECT convert(datetime, '20161023', 112) -- yyyymmdd
Found here: http://www.sqlusa.com/bestpractices/datetimeconversion/
This page on MSDN documentation lists all convert methods that LINQ to SQL does not support.
Convert.ToDateTime is not listed in there. So, I guess you could just use Convert.ToDateTime to do what you want.
This is not something typically for LINQ or any LINQ over Expression trees enabled provider (such as LINQ to SQL, LINQ to Entities, LINQ to NHibernate, LLBLGen Pro, etc, etc). This is simply a language question. You want to know how to convert the format yyyyMMdd to a DateTime.
The trick is to leave the conversion OUT of your LINQ (over Expression trees) query, because a LINQ provider will not be able to convert it, or if it can, you will get very provider specific implementation.
Therefore, the trick is to get it out of the database as a string (or of course even better: change your database model) and convert it to a DateTime in .NET. For instance:
// Doing .ToArray is essential, to ensure that the
// query is executed right away.
string[] inMemoryCollectionStrings = (
from item in db.Items
where some_condition
select item.Inv_Acctcur).ToArray();
// This next query does the translation from string to DateTime.
IEnumerable<DateTime> dates =
from value in inMemoryCollectionStrings
select DateTime.ParseExact(value, "yyyyMMdd",
CultureInfo.InvariantCulture);
In other words, you can use the following line to make the conversion:
DateTime.ParseExact(value, "yyyyMMdd", CultureInfo.InvariantCulture);
I am trying to create a LINQ query to return genres by movieid. The LINQ works in LINQPAD4. Can someone help me with the proper syntax? I am getting the following errors:
Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Linq.IQueryable'. An explicit conversion exists (are you missing a cast?)
and
Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.List'
Code:(note I have wrapped Title in the following line with parenthesis, but are actually brackets in my code.
public List(Genre) GetGenresByMovieId(string movieid)
{
var genres = from t in MovieCatalog.Titles
where t.Id == "BVlLx"
select t.Genres;
return genres.ToList();
}
The right query would look like
public IEnumerable<Genre> GetGenresByMovieId(string movieId)
{
return from title in ctx.Titles
from genre in title.Genres
where title.Id == "BVlLx"
select genre;
}
In the method call syntax, you need to use SelectMany, not Select, since the filter on titles returns a list of titles (which will always contain just one title, but the compiler doesn't know that) and so you want to "concatenate" all genres for each title in the results.
The return type is actually IQueryable, but if you only plan to enumerate over it, you can use IEnumerable, or call ToList() to force execution right there in the method (the way I wrote it the query would actually execute only once you try to enumerate it).
Your problem is your projection:
select new { Name = g.Name }
That is projecting the query into an anonymous type.
You need to project into the IQueryable you have declared (IQueryable<Genre>)
When working with LINQ queries, it's preferable to use implicitly-typed variables (var).
Also, not sure why you have that extra "from" in your query, you don't need that.
Something like this should work:
var genres = from t in MovieCatalog.Titles
where t.Id = "BVlLx"
select t.Genres;
return genres.ToList();
var genres should be typed to an IQueryable<Genre>.
That is assuming you want to return a collection of Genre objects.
If you just want the name, do this:
select t.Genres.Name
But that will return a collection of string objects (and var genres should be typed to an IQueryable<string>).
However, i have no idea about the NetFlix OData API, but that should get you on the right track.