I have a label to show BookName. I get it from table which name tblBooks. I don't know how to show Book Name into the label.
var query = from b in dc.tblBooks.Where(b=>b.BookID == 'B01') select b;
Can you help me know.
Your query as written will return a collection of books—IQueryable<Book>. If you're sure there will only be one result in this query, you can call SingleOrDefault, which will execute the query immediately and give you the actual book.
var Book = dc.tblBooks.Where(b => b.BookID == 'B01').SingleOrDefault();
if (Book != null)
myLabel.Text = Book.BookName;
Or you can simply say:
var Book = dc.tblBooks.SingleOrDefault(b => b.BookID == 'B01');
Which does the same thing.
If you're 110% sure there will always be a result, and you don't want to check for null, then you can use Single, which will do the same thing, except throw an exception if no results are found, where SingleOrDefault simple returns null.
var Book = dc.tblBooks.Single(b=>b.BookID == 'B01');
myLabel.Text = Book.BookName;
Try:
label.Text = query.FirstOrDefault().BookName;
Related
'''
QuestionModel getQuestionModelFromDatasnapshot(
DocumentSnapshot questionSnapshot) {
QuestionModel questionModel = new QuestionModel();
questionModel.question = questionSnapshot.data()'question'];
List<String> options = [
questionSnapshot.data()["option1"],
questionSnapshot.data()["option2"],
questionSnapshot.data()["option3"],
questionSnapshot.data()["option4"]
];
options.shuffle();
questionModel.option1 = options[0];
questionModel.option2 = options[1];
questionModel.option3 = options[2];
questionModel.option4 = options[3];
questionModel.correctOption = questionSnapshot.data()["option1"];
questionModel.answered = false;
print(questionModel.correctOption.toLowerCase());
return questionModel;
}
'''
It looks like you're using dart with null safety on and you are accessing a list or map that might be null. It's hard to tell from your code, but I'm guessing the offending line is
questionModel.correctOption = questionSnapshot.data()["option1"];
It might be one of the other [] calls earlier in your code (such as
questionSnapshot.data()["option1"]), but the solution is the same.
The problem is that questionSnapshot.data() might return null, and the compiler is flagging it.
If you are sure the data is not null, you can use the ! operator, like this:
questionModel.correctOption = questionSnapshot.data()!["option1"];
Another solution is a conditional null-safe operator ?, with a default value. In this case, the code would look like this:
questionModel.correctOption = questionSnapshot.data()?["option1"]??"DefaultValue;
But I would recommend checking if the returned data is null. It's easier for others to read and can be logged more easily:
var data = questionSnapshot.data();
if (data != null) {
questionModel.correctOption = data["option1"];
}
else {
//do something in that case
}
I completely understand that this is because LINQ query requires the whole expression to be translated to a server , and therefore I cant call an outside method in it. but as I have looked at other answers there is not relative solution to this. the only approach that I thought about is to loop through all the items in the model and than passing them to the query one by one but even though this approach would not help so I am seeking help in here for anyone to help me to figure out how to call a method or a way of calling a method appendstr that initializes a.PostedDate before checking its actual equivalent value in the giving LINQ Query.
[HttpGet]
public ActionResult SearchResult(int? page, string searchTitle = null, string searchLocation = null, string last24 = "")
{
ViewBag.searchTitle = searchTitle;
ViewBag.searchLocation = searchLocation;
ViewBag.page = page;
ViewBag.last24 = last24;
setUpApi(searchTitle, searchLocation);
var result = new List<AllJobModel>().AsQueryable();
if (!string.IsNullOrEmpty(ViewBag.searchTitle) || !string.IsNullOrEmpty(ViewBag.searchTitle) || !string.IsNullOrEmpty(ViewBag.last24))
{
setUpApi(searchTitle, searchLocation);
DateTime now = DateTime.Now;
result = db.AllJobModel.Where(a => a.JobTitle.Contains(searchTitle) && a.locationName.Contains(searchLocation) &&
appendstr(a.PostedDate).Equals(now.AddHours(-24).ToString("MM-dd-yyyy")));
}
else
{
result = from app in db.AllJobModel select app;
}
return View(result.ToList().ToPagedList(page ?? 1, 5));
}
The second method that gets called in the LINQ Query
public string appendstr(string str)
{
var x = str.Split(' ');
return 01 + "-" + x[1] + "-" + x[2];
}
I think you already understand that the .NET code you write in the Where clause is actually an expression that is parsed and converted to SQL. So if you have a funky string manipulation method, you can't use it directly.
The brute force option, as you seem to already understand, it to materialize the query first and then run the C# code over the results. You can do this with ToList() or AsEnumerable().
result = db.AllJobModel
.Where
(
a => a.JobTitle.Contains(searchTitle)
&& a.LocationName.Contains(searchLocation)
)
.AsEnumerable()
.Where
(
a => appendstr(a.PostedDate).Equals(now.AddHours(-24).ToString("MM-dd-yyyy")))
);
However in your specific case you can try a trick. You are attempting a date comparison, which SQL is perfectly capable of doing... you just need to convert that funky PostedDate to a SQL DateTime so that you can compare it directly. The gimmick for that is to use SqlFunctions.DateAdd to add null interval (e.g. 0 days). This implicitly converts the string to DateTime, where you can now query on the SQL side:
var targetDate = DateTime.Now.AddHours(-24);
result = db.AllJobModel
.Where
(
a => a.JobTitle.Contains(searchTitle)
&& a.LocationName.Contains(searchLocation)
&& SqlFunctions.DateAdd("DAY", 0, a.PostedDate) == targetDate
);
Credit goes to this post for the workaround.
var query = from c in context.Albums
where c.AlbumID in albumIds
select c.Albumname;
Here albumIds is IENUM<> of some custom type(in my case its an Entity)
When I do the above query I get an error
Operator == cannot be applied to type int and IEnumerable
This error is acceptable but how do I overcome this
Turn it around slightly - you want to check whether your enumerable of album ids contains the id of an album you have just iterated to in your linq. So something like this ...
albumIds = {1,2,13,25,277,567};
var query = context.Albums.Where(x=> albumIds.Contains(x.ID));
(Sorry, writing example code without a tool in front of me so forgive any obvious mistakes. Hopefully you can get the idea from this though).
var albumIds= new string[] { "900", "801", "802", "803","906" };
var lstData = context.tbl.Where(
x => (x.TimeCreated >= yesterday && x.TimeCreated < today) &&
albumIds.Contains(x.TransactionSetId)
).Select(x => x.X12_Interchange).ToList();
hi guys i am stuck converting below sql to LINQ query.
all i want is to have maximum number from list of (FA-00001 ,FA-00059)
SELECT MAX(CAST(SUBSTRING(ReferenceId, PATINDEX('%-%', ReferenceId) + 1, LEN(ReferenceId) - PATINDEX('%-%', ReferenceId)) AS int)) AS MaxReferenceId FROM [ClientRC].[dbo].[EHO_Action]
is this possible to convert to LINQ? thanks
An alternative approach using anonymous projection:
var y = (from record in
(from record in db.ClientRC
select new
{
Group = "x",
ReferenceNumber = Convert.ToInt32(record.ReferenceId.Split('-')[1])
})
group record by new { record.Group } into g
select new
{
MaxReferenceId = g.Max(p => p.ReferenceNumber)
});
http://msdn.microsoft.com/en-us/library/bb386972.aspx
var myvar = (from v in db.object where v!=null select v.id).Max();
MSDN has lots of examples for stuff like this.
Or, you can execute queries directly against a datacontext if you're using entity framework. Just make sure if you're doing anything with parameters you're parameterizing the query and not taking user input directly into it.
http://msdn.microsoft.com/en-us/library/ee358769.aspx
Try this..
var list = DBContext.EHO_Action
.Where(x => x.YourListColumn != null)
.Select(x => x.YourListColumn).ToList(); // Take the list (FA-00001 ,FA-00059) from db to a list
var maxNo = list.Max(x => Convert.ToInt32(x.Split('-')[1]));
Please change the context and column names according to your Linq context.
If you want to use sql you can do it this way..
var list = DBContext.ExecuteQuery<string>("select yourreqrdcolumn from [ClientRC].[dbo].[EHO_Action]");
How do I modify the query below to properly handle the case where the "Summary" element is missing from one of the articles? Now when that happens I get an "Object reference not set to an instance of an object."
var articles = from article in xmlDoc.Descendants("Article")
select new {
articleId = article.Attribute("ID").Value,
heading = article.Element("Heading").Value,
summary = article.Element("Summary").Value,
contents = article.Element("Contents").Value,
cats = from cat in article.Elements("Categories")
select new {
category = cat.Element("Category").Value
}
};
The problem is that article.Element("Summary") returns null if the element is not found, so you get a NullReferenceException when you try to get the Value property.
To solve this, note that XElement also has an explicit conversion to string. This won't throw if the XElement is null - you will just get a null string reference.
So to solve your problem you can change this:
summary = article.Element("Summary").Value,
to this:
summary = (string)article.Element("Summary")