Develop Reference

Entity Framework aliasing in join operation

I am creating a query in Visual Studio for retrieving data from a SQL Server.
Can I, and if so how, use aliasing on variables in .Join()s?
I have something like:
var query =
context.tblOne
.Join(
context.tblTwo,
varOne => varOne.ParamFromVarOne,
varTwo => varTwo.ParamFromVarTwo,
(varOne, varTwo) => varOne)
Can I somehow access the "varOne" and "varTwo" objects and their parameters outside of the join? I need other parameters from varOne and two in my .Where() clause to filter the search result.
Is there perhaps another way to query for this?
I have 10 .Join()s and on those joins and after the .Where() I want to create a new JSON object.toList() using the
.Select(x => new {x.param1, x.param2, x.param3}) etc
A more abstract way of explaining what I want to do is something like:
.Where(x => x.Param1 <= compareVariable1 &&
x.Param2 >= compareVariable1 &&
y => y.Param1 == compareVariable2 &&
z => z.Param1 == compareVariable3)
In other words, a .Where() clause with multiple table-records from which I compare the column values to method parameters/arguments.
Can I perhaps concatenate the Joins and if so how do I go about this?

Where Clauses Causing Errors in LINQ

I am trying to return rows based on a search term that may include a space.
The code below is is generating the following error. I cannot figure out what I'm doing wrong, any suggestions?
Local sequence cannot be used in LINQ to SQL implementations of query
operators except the Contains operator.
var searchTerms = term.Split(' ').ToList();
var surveys = (from s in dc.BasicNeedsSurveys where s.Hidden ==
false orderby s.CreatedOn descending select s)
.Where(x => searchTerms.Any(y => y.Contains(x.FirstName))
|| searchTerms.Any(y => y.Contains(x.LastName))
|| searchTerms.Any(y => y.Contains(x.FEMANumber)));

according to the error message you are using linq to sql (or EF). linq to sql generate SQL query behind the scene, and you cant use a local var such as searchTerms inside an sql query. if i understand it correctly and dc.BasicNeedsSurveys is actually a data base entity (like in entity framework for example) your solution will be to first execute the sql query and then run the test if substring of search terms contains the search result. ToList is one function that can do that.
var searchTerms = term.Split(' ').ToList();
var surveys = (from s in dc.BasicNeedsSurveys where s.Hidden ==
false orderby s.CreatedOn descending select s)
.ToList()
.Where(x => searchTerms.Any(y => y.Contains(x.FirstName))
|| searchTerms.Any(y => y.Contains(x.LastName))
|| searchTerms.Any(y => y.Contains(x.FEMANumber)));
of course, there might be better ways to do that with better performance since here you are filtering the results only after you read all of them from the hard drive, but there is really not enough information in the question for that

How to get data from linq query using select

I'm testing a simple LINQ select query and want to get two DateTime values from the table, but I'm doing something wrong here and need to know what I'm doing/thinking wrong?
My query:
var test = from x in db.Projects where x.ID == 1 select x;
Then I try to get on of the values like this:
DateTime Date = test. ?????
Here I thought I should get a suggestion from the Intellisense after the dot to pick the value from the column StartDate the table, but this isn't working.

If you need multiple matches...
Are you sure that you have multiple Project objects that have the same ID of 1 which your query currently suggests? If that is the case, then your query should return all of the records that meet that constraint via the Where() method :
// Get your Projects that meet your criteria
var test = db.Projects.Where(p => p.ID == 1);
If you need to access properties from these elements, you could either loop through them explicitly :
// Iterate through each match that was found
foreach(var t in test)
{
// Access your properties here
DateTime dt = t.YourDateProperty;
}
Or you could accomplish this using a Select() statement to only pull the properties that you need :
// This will return a collection of Dates mapped from each element in your collection
var testDates = db.Projects.Where(p => p.ID == 1)
.Select(x => x.YourDateProperty);
If you only need a single match...
If you only need to match a single element within your collection, you might consider using the First(), Single() or their equivalent FirstOrDefault() and SingleOrDefault() methods, which will return a single entity that you can use as expected :
// This will return the first Project with an ID of 1
var test = db.Project.FirstOrDefault(p => p.ID == 1);
// If it was successful
if(test != null)
{
// Then you can safely access it here
DateTime dt = test.YourDateProperty;
}
The only difference between the methods mentioned (normal vs OrDefault()) is that the OrDefault() methods will return null if no matching elements are found, so they generally require a null check as seen above.

test is going to be an enumeration (IEnumerable<>, IQueryable<>, etc... many are applicable) of your Project type. So if, for example, you want the first record, you might do this:
DateTime Date = test.First().SomeDateProperty;
All of the data returned from your query is in test. It could be zero records, one record, many records, etc.

In test you will have a collection which matches the condition x.ID == 1. You should iterate through that collection and take your needed properties.
Edit
I suggest you to use the syntax:
var result = db.Projects.FirstOrDefault(x => x.ID ==1);

this is such as:
var date = test.FirstOrDefault();
DateTime? Date = date != null ? date.StartDate : null;

Sitecore: efficient way to use LINQ to compare against an ID

I have a LINQ query retrieving a list of , such as this:
var results = SearchContext.GetQueryable<Person>()
.Where(i => i.Enabled)
.Where(i => i.TemplateName == "Person")
.Random(6);
Each object of type "Person" has a "Location" field which is also a Glass mapped item, and hence has an ID; I would like to only select items whose Location has a specific ID.
How can I go about doing this in an efficient manner?
EDIT: I should probably clarify that I am unable to perform this comparison, efficiently or not. Because the GUID is an object and I cannot perform ToString in a LINQ query, I am unable to only pick the items whose Location item has a specific ID. Any clues on how this could be achieved?
EDIT 2: Adding the clause
.Where(i => i.Location.Id == this.Id)
Doesn't work, for... some reason, as I'm unable to debug what LINQ "sees". If I convert the other ID I'm comparing it against to string this way:
var theOtherID = this.Id.ToString("N");
Then it works with this LINQ line:
.Where(i => i["Location"].Contains(theOtherID))
I still have no idea why.

One approach is to include a separate property on Person that is ignored by Glass mapper, but can be used in searches:
[SitecoreIgnore]
[Sitecore.ContentSearch.IndexField("location")]
public Sitecore.Data.ID LocationID { get; set; }
You can use this in your search as follows:
Sitecore.Data.ID locationId = Sitecore.Data.ID.Parse(stringOrGuid);
var results = SearchContext.GetQueryable<Person>()
.Where(i => i.Enabled)
.Where(i => i.TemplateName == "Person")
.Where(i => i.LocationID == locationId)
.Random(6);
I think the efficiency of using multiple where clauses vs. conditionals is debatable. They will likely result in the same Lucene query being performed. I would prefer readability over optimization in this instance, but that's just me.

I can't think of a more efficient methods than using a simple where statement like in:
var results = SearchContext.GetQueryable<Person>()
.Where(i => i.Enabled && i.TemplateName == "Person" &&
i.Location != null && i.Location.Id == 1)
.Random(6);
Keep in mind that if you use the && statement instead of a where for each parameter, you reduce the complexity of the algorithm.
You could also use an Inverse Navigation Property on Location to a virtual ICollection<Person> and then be able to do this:
var results = SearchContext.GetQueryable<Location>()
.Where(i => i.Id == 1 && i.Persons.Where(p => p.Enabled && p.TemplateName == "Person").Any())
.Random(6);
The first option would still be the most efficient, because the second one uses sub-queries. But it is worth knowing you can do your search the other way.

Why Reverse() cannot be converted into SQL?

My application is running under ASP.NET 4.0, which uses BLToolkti as ORM tool.
I have some queryable expression:
var q = db.GetTable<T>()
.Where(tb=>tb.TeamId==MyTeamId && tb.Season==MySeasonId)
.OrderByDescending(tb=>tb.Id)
.Take(20)
.Reverse()
Attempt to convert q.ToList() causes the following error:
Sequence 'Table(TeamBudget).Where(tb => ((tb.TeamId ==
value(VfmElita.DataLogicLayer.Teams.Team+TeamBudget+<>c__DisplayClass78).teamId)
AndAlso (tb.Season ==
value(VfmElita.DataLogicLayer.Teams.Team+TeamBudget+<>c__DisplayClass78).season))).OrderByDescending(tb
=> Convert(tb.Id)).Take(20).Reverse()' cannot be converted to SQL.
If I remove ".Reverse()" from the queryable object everything works fine.
What is the reason why queryable object with .Reverse() cannot be converted into SQL? Is that BLToolkit limitation? Is there any solution workaround for that?
Thank you!

It's pretty clear what the other LINQ methods convert to (where, order by, top(20)), but what would Reverse() convert to? I can't think of an SQL statement I've seen that mimics that behavior, and when you're querying the database your LINQ statement must ultimately resolve to valid SQL.
This may not be what you're going for, but one option would be to execute the query first using ToList(), then apply Reverse():
var q = db.GetTable<T>()
.Where(tb => tb.TeamId == MyTeamId && tb.Season == MySeasonId)
.OrderByDescending(tb => tb.Id)
.Take(20)
.ToList()
.Reverse();
Alternatively, you could get the count and skip that many records first, although this could be inaccurate if the number of records change between calls. Plus it's two queries instead of just one.
var totalRecords = db.GetTable<T>()
.Count(tb => tb.TeamId == MyTeamId && tb.Season == MySeasonId);
var q = db.GetTable<T>()
.Where(tb => tb.TeamId == MyTeamId && tb.Season == MySeasonId)
.Order(tb => tb.Id)
.Skip(totalRecords)
.Take(20);