Write this SQL query to Entity Framework lambda expression or other way

Question

db.DbEnquiryModules - how to write this query as a lambda expression or linq?

SELECT  
    tenq.EnquiryID
    ,tenq.EnquiryNo
    ,tenq.CompanyID
    ,tenq.EnquiryDate
    ,tenq.ClientID
    ,tenq.Address
    ,tenq.ContactPerson
    ,tenq.Email
    ,tenq.Mobile
    ,tenq.Landline
    ,tenq.SourceID
    ,tenq.PriorityID
    ,tenq.AreaID
    ,tenq.status
    ,tenq.Remark
    ,tenq.IsDeleted
    ,tenq.CreatedDate
    ,tenq.CreatedBy
    ,tenq.ModifiedDate
    ,tenq.ModifiedBy
    ,Y.FollowupDate AS LastFollowup
    ,Y.NextFollowup AS NextFollowup
    ,srno2
INTO
    #tmp 
FROM
    tblEnquiryModule tenq
LEFT JOIN 
   (SELECT 
        ROW_NUMBER() OVER (PARTITION BY EnquiryModuleID ORDER BY FollowupId DESC) SRno2,
        * 
    FROM
        tblFollowup) Y ON Y.EnquiryModuleID = EnquiryID
                       AND Y.srno2 <=2  ----------Last followUp
WHERE
    tenq.CompanyID = @companyid


--

DELETE a
FROM #tmp a
JOIN #tmp b ON a.EnquiryID = b.EnquiryID
            AND b.srno2 = 2
WHERE a.srno2 = 1 

SELECT * FROM #tmp 

I have two tables with enquiry and its followup.above query returns enquiry with its last followup date if present and next followup date

My entity

public class DTOEnquiryModule
{   [Key]
    public int EnquiryID { get; set; }
    public string EnquiryNo { get; set; }
    public int CompanyID { get; set; }
    public DateTime? EnquiryDate { get; set; }
    public string Mobile { get; set; }
    public string Landline { get; set; }
    public string status { get; set; }
    public int? ModifiedBy { get; set; }}  

public class DTOFollowup
{
    [Key]
    public int FollowupId { get; set; }
    public int EnquiryModuleID { get; set; }
    [ForeignKey("EnquiryModuleID")]
    public DTOEnquiryModule EnquiryModule { get; set; }
    public DateTime FollowupDate { get; set; }
    public string FollowupRemark { get; set; }
    public DateTime? NextFollowup { get; set; }
    public string NextFollowupRemark { get; set; }
}

Enquiry Table

|EnquiryID|EnquiryNo|EnquiryDate            |status 
|1        |EN1      |2019-02-19 00:00:00.000|ongoing
|2        |EN2      |2019-02-20 00:00:00.000|ongoing
|3        |EN3      |2019-02-23 00:00:00.000|ongoing

Followup table

FollowupId|EnquiryModuleID|FollowupDate           |FollowupRemark|NextFollowup 
1         |1              |2019-02-20 00:00:00.000|NA            |NULL
2         |2              |2019-02-21 00:00:00.000|NA            |2019-02-23 00:00:00.000
3         |2              |2019-02-23 00:00:00.000|NA            |NULL
4         |3              |2019-02-24 00:00:00.000|NA            |2019-02-26 00:00:00.000
5         |3              |2019-02-26 00:00:00.000|NA            |2019-02-28 00:00:00.000
6         |3              |2019-02-28 00:00:00.000|NA            |NULL

I want below result table

|EnquiryID|EnquiryNo|EnquiryDate            |status |NextFollowup           |LastFollowup
|1        |EN1      |2019-02-19 00:00:00.000|ongoing|NULL                   |2019-02-20 00:00:00.000
|2        |EN2      |2019-02-20 00:00:00.000|ongoing|2019-02-23 00:00:00.000|2019-02-21 00:00:00.000
|3        |EN3      |2019-02-23 00:00:00.000|ongoing|2019-02-28 00:00:00.000|2019-02-26 00:00:00.000

When ever i am added new followup, need to update previous follow up details for maintain history and get latest followup by enquiry id.

I want to show enquiry listing with last followup and next followup date

Answer 1

So you have tables with Enquiries and FollowUps . Every Enquiry has zero or more FollowUps , every FollowUp belongs to exactly one `Enquiry, using a foreign key: A straightforward one-to-many relation.

If you'd followed the entity framework code first conventions, you would have had classes like:

class Enquiry
{
    public int Id {get; set; }
    public string EnquiryNo { get; set; }
    public DateTime? EnquiryDate { get; set; }
    public string status { get; set; }
    ...

    // every Enquiry has zero or more FollowUps (one-to-many)
    public virtual ICollection<FollowUp> FollowUps {get; set;}
}

class FollowUp
{
    public int Id {get; set; }
    public DateTime FollowupDate { get; set; }
    ...

    // every FollowUp belongs to exactly one Enquiry, using foreign key
    public int EnquiryId {get; set;}
    public virtual Enquiry Enquiry {get; set;}
}

For completeness the DbContext:

class MyDbContext : DbContext
{
    public DbSet<Enquiry> Enquiries {get; set;}
    public DbSet<FollowUp> FollowUps {get; set;}
}

Because I followed the conventions, this is all that entity framework needs to know to detect your tables, the columns in your tables and the relation between the tables. Only if you want different identifiers you'll need Attributes or fluent API. The important part of this is that I specify the one-to-many by using virtual properties

In entity framework the columns are represented by the non-virtual properties; the virtual properties represent the relations between the tables (one-to-many, many-to-many, ...)

Your requirement: "When ever i am added new followup, need to update previous follow up details".

I am added? need to update previous follow up? Maybe you should work on your requirement skills.

I think you meant the following:

Requirement Give me (some properties of) all Enquiries, with its newest FollowUpDate and its newest-but-one FollowupDate (which for some reason you decide to call the last date).

If an Enquiry has only one Followup, I want the EnquiryDate and the FollowUpdate. If the Enquiry has no followups, I only want the EnquiryDate.

So the collection of eligible FollowUpdates is the EnquiryDate + all FollowUpdates. Order them by Descending date and take the first two.

var result = dbContext.Enquiries.Select(enquiry => new
{
    EnquiryId = enquiry.Id,
    EnquiryNo = enquiry.EnquiryNo,
    EnquiryDate = enquiry.EnquiryDate,
    Status = enquiry.Status,

    // For the followups: take the followUp dates as nullable DateTime
    // and add the EnquiryDate
    FollowUps = enquiry.FollowUps
        .Select(followUp => followUp.FollowUpdate)
        .Cast<DateTime?>()
        .Concat(new DateTime?[] {enquiry.EnquiryDate})

        // take the two newest ones; we don't want null values
        .Where(date => date != null)
        .OrderByDescending(date => date)
        .Take(2)
        .ToList(),
})

// move this to local process, so you can use FollowUps to get Next / Last
.AsEnumerable()
.Select(fetchedData => new
{
    EnquiryId = fetchedData.EnquiryId,
    EnquiryNo = fetchedData.EnquiryNo,
    EnquiryDate = fetchedData.EnquiryDate,
    Status = fetchedData.Status,

    // FollowUps are ordered in Descending order. FirstOrDefault is the newest!
    NextFollowUp = enquiry.FollowUps.FirstOrDefault(),
    LastFollowUp = enquiry.FollowUps.LastOrDefault(),
}

Entity framework knows your one-to-many relation. It will translate your usage of the ICollection into a GroupJoin

If desired you can let your database management system do the selection of NextFollowUp and LastFollowUp. The number of transferred data will be the same, so this won't speed up your process.

Some people don't like to use the virtual ICollection to get the "Enquiries with their Followup's". You can do the GroupJoin yourself:

result = dbContext.Enquiries.GroupJoin(dbContext.FollowUps,
    enquiry => enquiry.Id,           // from each enquiry take the primary key
    followUp => followUp.EnquiryId,  // from each followUp take the foreign key

    // result selection: use each enquiry with all its matching followUps to make a new
    (enquiry, followUpsOfThisEnquiry) => new
    {
        EnquiryId = enquiry.Id,
        ... etc.

Keep your database normalized

You decided to add a DateTime column NextFollowUp in your database. This is not a good choice.

Id | FollowUpDate | NextFollowUpDate
01 |  2019-02-13  |  2019-02-14
20 |  2020-02-29  |     null

It seems to me that FollowUp [20] is the next FollowUp of FollowUp 1 . What happens if I change the date of FollowUp [20]:

Id | FollowUpDate | NextFollowUpDate
01 |  2019-02-13  |  2019-02-14
20 |  2019-02-14  |     null

Is this still correct? Is [20] suddenly not the next of [01]? Whenever you change a date you'll have to check all FollowUps to see if it points to this FollowUp.

And what about the following:

Id | FollowUpDate | NextFollowUpDate
04 |  2019-02-13  |  2019-02-14
05 |  2019-02-14  |     null
06 |  2019-02-14  |     null

Who is the Next of [04]?

Keep in mind that a followup is identified by its primary key, not by its date. The date of a followup might change. However this doesn't change the followup itself.

Id | FollowUpDate | NextFollowUpId
04 |  2019-02-13  |      05
05 |  2019-02-20  |      06
06 |  2019-02-14  |     null

After introducing you can safely change any property of the FollowUp, except of course its primary key. Before you decide to introduce the context of a "next follow up" you should think for yourself what it is: is it the next in date? Then you don't need a foreign key, you can order them by datetime