CODEWITHSUNDEEP
c#entity-frameworklistclassmethods
Alessandro Minneci
Alessandro Minneci

Reputation: 301

How to Convert to self created Entity Framework class?

I created a class with Entity Framework like this:

public class Lehrling
    {
       [Key]
       public int lehrling_id { get; set; }
       [Required]
       [StringLength(25)]
       public string vorname { get; set; }
       [Required]
       [StringLength(25)]
       public string nachname { get; set; }
    }

In my c# backend, i created a object of this class: Lehrling lehrling = new Lehrling(); now, i want to assign a method to my object lehrling like this: 

lehrling = dataMgr.GetLehrling(lehrlingID, requestedMd5key);

lehrlingID is type int and requestedMd5key is type string

The Method GetLehrling(lehrlingID, requestedMd5key) was created like this in my Datamanager.cs 

public List<Lehrling> GetLehrling(int lehrlingID, string md5key)
        {
            Uri weburi = new Uri(baseuri, API_LEHRLING + lehrlingID + '/' + md5key);

            try
            {
                HttpResponseMessage response = httpClient.GetAsync(weburi).Result;
                var json = response.Content.ReadAsStringAsync().Result;

                JavaScriptSerializer ser = new JavaScriptSerializer();
                List<Lehrling> data = ser.Deserialize<List<Lehrling>>(json);

                //Für Sortierung Wichtig

                return data;

            }
            catch (Exception)
            {
                throw;

            }
        }

as you can see it returns a List<Lehrling> data The Reason why i get a error message is clear, the method is type List<Lehrling> and the variable lehrling is type Lehrling

How can I fix this Error, any suggestions?

Upvotes: 1

Views: 50

Answers (2)

uTeisT
uTeisT

Reputation: 2266

Well, as you said you actually need multiple items:

    Lehrling lehrling = new Lehrling();

Needs to be

    List<Lehrling> lehrlingList = new List<Lehrling>();
    lehrlingList = dataMgr.GetLehrling(lehrlingID, requestedMd5key);

That should eliminate the error.

Upvotes: 1

Ruslan F.
Ruslan F.

Reputation: 5776

You should choose an item from collection.

lehrling = dataMgr.GetLehrling(lehrlingID, requestedMd5key).FirstOrDefault(l => some codition);

Or just take first one.

lehrling = dataMgr.GetLehrling(lehrlingID, requestedMd5key).FirstOrDefault();

Both variant may lead to NullPointerExeption if no items were in collection.

Upvotes: 1

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