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how to search record from single table with multiple parameters using LINQ?

I am trying to search record(s) from table by appying multiple search parameters.
as per below snap.
here by using various parameters as per above snap i want to filter the records.
here user could enter any combination of parameter(s) to search record.
i tried something like below code hich works for single condition but fails for combination of any search paramets.
public List<students> SearchStudents(students search)
{
var result = new List<students>();
var records= from stud in db.students
where stud.enrollmentNumber== search.enrollmentNumber
|| stud.enrollmentDate==search.enrollmenttDate
|| stud.enrollmentType==search.enrollmentType
|| stud.className==search.className
select new Search()
{
enrollmentNumber= stud.enrollmentNumber,
enrollmentDate = stud.enrollmentDate,
enrollmentType = stud.enrollmentType,
Name = stud.Name,
className=stud.className,
Description = stud.Description
};
result = records.ToList();
return result;
}
but this is not working properly. means it returns same result whatever parameters I pass.
Like in the table i ahve 20 records and the enrollment number is the unique value field in DB so here when i am passing enrollment number thats like "2018-0001" it returns all records when it should return only single reocrd.
can someone guide me with this?

Without further explanation in your question about how this isn't working, the best we can do is guess. However, one very plausible reason for this is because you're including parameters you don't want to be filtering on.
Because you're using ORs in your statement, if any of those other properties are defaulted in the database, you're going to be returning those records. What you need to be doing is conditionally including your pieces of the WHERE clauses for only the properties that you want to search on. Unfortunately, that is not possible with the "SQL syntax" version of LINQ, so you will need to convert your query to that. (Good news: It's slightly more performant as well as it usually has to convert the SQL to the method syntax.)
Because of deferred execution, your query will not be sent to the database until you call a .ToList() or something to actually start processing the results. This allows you to chain method calls together, even if they are completely different C# statements. This is what you'll want to do:
public List<students> SearchStudents(students search)
{
var query = db.students;
if (!string.IsNullOrWhiteSpace(search.enrollmentNumber))
{
query = query.Where(s => s.enrollmentNumber == search.enrollmentNumber);
}
if (search.enrollmentDate != DateTime.MinValue)
{
query = query.Where(s => s.enrollmentDate == search.enrollmentDate);
}
if (!string.IsNullOrWhiteSpace(search.enrollmentType))
{
query = query.Where(s => s.enrollmentType == search.enrollmentType);
}
if (!string.IsNullOrWhiteSpace(search.className))
{
query = query.Where(s => s.className == search.className);
}
return query.Select(stud => new Search
{
enrollmentNumber= stud.enrollmentNumber,
enrollmentDate = stud.enrollmentDate,
enrollmentType = stud.enrollmentType,
Name = stud.Name,
className=stud.className,
Description = stud.Description
})
.ToList();
}
You may need to adjust the if statements in there to accommodate different data types than what is intuitive from the names, but this will only add the filter if a value has been provided.

LINQ2SQL select rows based on large where

I'm searching for a bunch of int32's in a SQL (Compact edition) database using LINQ2SQL.
My main problem is that I have a large list (thousands) of int32 and I want all records in the DB where id field in DB matches any of my int32's. Currently I'm selecting one row at the time, effectively searching the index thousands of times.
How can I optimize this? Temp table?

This sounds like you could use a Contains query:
int[] intArray = ...;
var matches = from item in context.SomeTable
where intArray.Contains(item.id)
select item;

For serarching for thousands of values, your options are:
Send an XML block to a stored procedure (complex, but doable)
Create a temp table, bulk upload the data, then join onto it (can cause problems with concurrency)
Execute multiple queries (i.e. break your group of IDs into chunks of a thousand or so and use BrokenGlass's solution)
I'm not sure which you can do with Compact Edition.

Insert your ints in a SQL table then do :
var items = from row in table
join intRow in intTable on row.TheIntColumn equals intRow.IntColumn
select row;
Edit 1 & 2: Changed the answer so he joins 2 tables, no collections.

My Preference would be to writing a Stored Procedure for the search. If you have an Index on the field that you are searching, It would make life a lot easier for you in the future when the amount of rows to process increases.
The complexity you will come across is writing a select statement that can do an IN Clause from an input parameter. What you need is to have a Table-Valued function to convert the string (of Id's) into a Column and use that column in the IN Clause.
like:
Select *
From SomeTable So
Where So.ID In (Select Column1 From dbo.StringToTable(InputIds))

I've come up with this linq solution after being tired of writing manual batching code.
It's not perfect (i.e. the batches are not exactly perfect) but it solves the problem.
Very useful when you are not allowed to write stored procs or sql functions. Works with almost every linq expression.
Enjoy:
public static IQueryable<TResultElement> RunQueryWithBatching<TBatchElement, TResultElement>(this IList<TBatchElement> listToBatch, int batchSize, Func<List<TBatchElement>, IQueryable<TResultElement>> initialQuery)
{
return RunQueryWithBatching(listToBatch, initialQuery, batchSize);
}
public static IQueryable<TResultElement> RunQueryWithBatching<TBatchElement, TResultElement>(this IList<TBatchElement> listToBatch, Func<List<TBatchElement>, IQueryable<TResultElement>> initialQuery)
{
return RunQueryWithBatching(listToBatch, initialQuery, 0);
}
public static IQueryable<TResultElement> RunQueryWithBatching<TBatchElement, TResultElement>(this IList<TBatchElement> listToBatch, Func<List<TBatchElement>, IQueryable<TResultElement>> initialQuery, int batchSize)
{
if (listToBatch == null)
throw new ArgumentNullException("listToBatch");
if (initialQuery == null)
throw new ArgumentNullException("initialQuery");
if (batchSize <= 0)
batchSize = 1000;
int batchCount = (listToBatch.Count / batchSize) + 1;
var batchGroup = listToBatch.AsQueryable().Select((elem, index) => new { GroupKey = index % batchCount, BatchElement = elem }); // Enumerable.Range(0, listToBatch.Count).Zip(listToBatch, (first, second) => new { GroupKey = first, BatchElement = second });
var keysBatchGroup = from obj in batchGroup
group obj by obj.GroupKey into grouped
select grouped;
var groupedBatches = keysBatchGroup.Select(key => key.Select((group) => group.BatchElement));
var map = from employeekeysBatchGroup in groupedBatches
let batchResult = initialQuery(employeekeysBatchGroup.ToList()).ToList() // force to memory because of stupid translation error in linq2sql
from br in batchResult
select br;
return map;
}
usage:
using (var context = new SourceDataContext())
{
// some code
var myBatchResult = intArray.RunQueryWithBatching(batch => from v1 in context.Table where batch.Contains(v1.IntProperty) select v1, 2000);
// some other code that makes use of myBatchResult
}
then either use result, either expand to list, or whatever you need. Just make sure you don't lose the DataContext reference.

Linq to SQL Updating Data

I am just starting to use linq to sql for data access. It is working fine for read only. But it does not work for update. I have been reading the threads over several forums. It is clear that anonymous types (in my case var) cannot be updated. I cannot find what I should replace the var with and where I find it. I will appreciate any help.
Below is the code. The exception is
Error 1 Property or indexer 'AnonymousType#1.date_last_logon' cannot be assigned to -- it is read only
fmcsaDataContext db = new fmcsaDataContext();
// DataTable _UserTable;
UserModel _UserModel = new UserModel();
var users = from u in db.FMCSA_USERs
where u.USER_NAME == pName && u.ACTIVE == true
select new
{
date_last_logon = u.DATE_LAST_LOGON,
date_current_logon = u.DATE_CURRENT_LOGON,
failed_login = u.FAILED_LOGIN,
};
if (users.Count() == 0)
return null;
foreach (var user in users)
{
user.date_last_logon = user.date_current_logon;
}

This is the case for any ORM tool; you will have to use the entity types that LINQ-to-SQL generates for you when you make your .dbml file if you want to perform CRUD operations.
Also, be aware that your query is being executed twice and is not concurrently safe; calling Count() executes your query with a Count aggregate in the database, then looping over it executes the query again, this time bringing back results. Given what you're doing, this may be better:
var users = (from u in db.FMCSA_USERs
where u.USER_NAME == pName && u.ACTIVE == true
select u).ToList(); // This executes the query and materializes
// the results into a List<FMCSA_USER>
if (users.Count == 0) return null;
foreach (var user in users)
{
user.date_last_logon = user.date_current_logon;
}
db.SaveChanges();

In order to update data, you cannot use anonymous types.
Instead, you can end your query with select u; to select the actual entities.

Table you are trying to update using LINQ, should have Primary key.

Avoid "Nullable object must have a value." in Linq-To-Sql

I have a method query like this:
public IList<BusinessObject> GetBusinessObject(Guid? filterId)
{
using (var db = new L2SDataContext())
{
var result = from bo in db.BusinessObjects
where (filterId.HasValue)
? bo.Filter == filterId.value
: true
orderby bo.Name
select SqlModelConverters.ConvertBusinessObject(bo);
return result.ToList();
}
}
At runtime, this throws a System.InvalidOperationException: Nullable object must have a value.
Looking at the Debugger, the problem is my Where Clause: Linq To SQL tries to convert the entire thing to SQL, so even if filterId is NULL, it will still try to access filterId.value.
I thought/hoped the C# compiler/CLR would evaluate that where clause as a code block and only send one of the two branches to Linq To SQL, but that's not how it works.
My refactored version works, but is not very elegant:
public IList<BusinessObject> GetBusinessObject(Guid? filterId)
{
using (var db = new L2SDataContext())
{
var temp = from bo in db.BusinessObjects select bo;
if(filterId.HasValue) temp = temp.Where(t => t.Filter == filterId.Value);
var result = from t in temp
orderby t.Name
select SqlModelConverters.ConvertBusinessObject(bo);
return result.ToList();
}
}
I know that Lazy-Evaluation will make sure that only one query is really sent, but having that temp object in there isn't that great really.

Did you try:
where filterId == null || t.Filter == filterId

Your fix is exactly correct. You are effectively trying to build up a query dynamically, based on your function input. It's a good idea to omit the where clause instead of supplying WHERE TRUE anyway. If I were writing this query, I would go with your fixed version myself.
It's not as pretty as using the language keywords, but it's still the right way to approach the query in my opinion.

LINQ: Paging technique, using take and skip but need total records also - how to implement this?

I have implemented a paging routine using skip and take. It works great, but I need the total number of records in the table prior to calling Take and Skip.
I know I can submit 2 separate queries.
Get Count
Skip and Take
But I would prefer not to issue 2 calls to LINQ.
How can I return it in the same query (e.g. using a nested select statement)?
Previously, I used a paging technique in a stored procedure. I returned the items by using a temporary table, and I passed the count to an output parameter.

I'm sorry, but you can't. At least, not in a pretty way.
You can do it in an unpretty way, but I don't think you like that:
var query = from e in db.Entities where etc etc etc;
var pagedQuery =
from e in query.Skip(pageSize * pageNumber).Take(pageSize)
select new
{
Count = query.Count(),
Entity = e
};
You see? Not pretty at all.

There is no reason to do two seperate queries or even a stored procedure. Use a let binding to note a sub-query when you are done you can have an anon type that contains both your selected item as well as your total count. A single query to the database, 1 linq expression and your done. TO Get the values it would be jobQuery.Select(x => x.item) or jobQuery.FirstOrDefault().Count
Let expressions are an amazing thing.
var jobQuery = (
from job in jc.Jobs
let jobCount = (
from j in jc.Jobs
where j.CustomerNumber.Equals(CustomerNumber)
select
j
).Count()
where job.CustomerNumber.Equals(CustomerNumber)
select
new
{
item = job.OrderBy(x => x.FieldName).Skip(0).Take(100),
Count = jobCount
}
);