CODEWITHSUNDEEP
c#linq
Hassan Shabbir
Hassan Shabbir

Reputation: 23

Convert Foreach into linq Expression

I am trying to get list of devices against a current customer from a Device table. I did it but with a foreach loop, but I wanted to do it operation using linq, instead.

here is my class structure

public class Device
{
    public string type { get; set; }
    public int id { get; set; }
    public List<Role> roles { get; set; }
}


public class Role
{
    public int roleId { get; set; }
    public string roleName { get; set; }
    public int customerId { get; set; }
}

Here is my Code

var devList = list.Where(x => x.type == "device1").ToList();

foreach (var item in devList)
{
    if (item.roles != null)
    {
        var kss = item.roles.Where(z => z.customerId == kunId).FirstOrDefault();
        if (kss != null)
        {
            m.devicesList.Add(item);
        }
    }
}

I need to get devices against the current customer, so I have to compare my current user id with customerId.

How can I convert this to linq-to-sql?

Upvotes: 0

Views: 806

Answers (4)

Harald Coppoolse
Harald Coppoolse

Reputation: 30512

So you have an object kunId, which is of the same type as Role.CustomerId. You also have a sequence of Items in object devList. And finally, you also have a property m.DevicesList, which implements ICollection<Item> (= you have a method Add(Item))

Your current method checks every Item from your sequence of Items. If property Roles is null, you ignore the Item. If, on the other hand, you have some Roles, you get the first or default Role that has a value for property CustomerId that equals kunId. If there is such a non-default Role, then you add the Item to m.DevicesList.

I'll rephrase this requirement.

If and only if an Item has a non-null value for property Roles, and at least one of these Roles has a value for property CustomerId that equals kunId, then you add the Item to the sequence of Items in m.DevicesList

var itemsToAddToMDevicesList = devList.Where(item => 
    item.Roles != null &&
    item.Roles.Where(role => role.CustomerId == kunId).Any();

In words: the sequence of Items that you want to add to m.DeviceList is the sequence of all Items in devList that has a non-null value for property Roles, and has at least one Role in property Roles that has a value for property CustomerId that equals kunId.

Upvotes: 1

Joel Coehoorn
Joel Coehoorn

Reputation: 416149

There are two ways to approach this.

First, you could put everything into a complicated Where operation:

var devices = list.Where(d => d.type == "device1" && d.roles is object && d.roles.Any(r => r.customerId == kunId) );

Second, you could spread it out over multiple separate operations, but each operation is much easier to understand:

var devices = list.Where(d => d.type == "device1").
                   Where(d => d.roles is object).
                   Where(d => d.roles.Any(r => r.customerId == kunId) );

The performance will be similar for either option. There is overhead for the additional Where() calls, but not as much as you might think... the JITter can do some amazing things with this kind of code, and I wouldn't be surprised to see both of these end up with the exact same IL.

Also notice in both cases there is no ToList() call. You can very often greatly improve performance and memory use by sticking with IEnumerable for longer.

At this point, it's unclear to me from the question whether you are merely appending into the existing m.devicesList or whether these values can replace whatever might currently be in that collection.

Assuming m.devicesList is declared as List<Device> (or similar), the former option would look like this:

m.devicesList.AddRange(devices);

Again, there was no need to ever call ToList().

The latter would look like this:

m.devicesList = devices.ToList();

We could also combine both steps into a single statement. Here's one of the four possible combinations:

m.devicesList.AddRange(list.Where(d => d.type == "device1").
                            Where(d => d.roles is object).
                            Where(d => d.roles.Any(r => r.customerId == kunId) )
                      );

Upvotes: 3

Luis Costa Brochado
Luis Costa Brochado

Reputation: 151

You should be able to remove the .ToList() at the end of the linq expression value you're assigning to devList.

Additionally, if you're aiming to optimize the operation you're performing, you might consider maintaining the current code, instead of converting it to a linq expression.

Still, if you need to convert the foreach loop, have a look at the official microsoft documentation, you should be able to do it automatically with the help of intellisense.

Upvotes: 0

cly
cly

Reputation: 708

Always try to "implement" your requirements in plain natural language first.

What devices do you need? That ones which:

  1. have type of "device1"
  2. have role assigned with given customer

Construct each part separately, add necessary guards e.g. roles != null and you get something like this:

var devicesFound = list.Where(d => 
   d.type == "device1" && 
   d.roles != null && 
   d.roles.Any(r => r.customerId == kunId));

m.devicesList.AddRange(devicesFound);

Upvotes: 0

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