Updating List item from Event Receiver of another List

Question

According to my requirement, I've 2 Lists within the same site List A and List B. Below are the columns in List A: User [PeoplePicker], City [dropdown (2 choices)], Company [dropdown (5 choices)], Salary [dropdown]

Below are the columns in List B : User [PeoplePicker], City [dropdown (2 choices)], Company [dropdown (5 choices)]

there are already many items in List A and for an User no two items in List A are similar (criteria we don't need to worry about) so an User can have a total of 10 combinations. Now I want to trigger an Event Receiver using ItemAdded() in List B so that based on the values of those 3 columns (User, City, and Company) I can update the value of Salary in List A. Can anyone please help me to achieve this requirement?

Example: List A: User: Rolly Anand City: Delhi Company: Microsoft Salary: 2 Lakh

adding Item to List B: User: Rolly Anand City: Delhi Company: Microsoft

after adding the item to List B that Salary should change in List A: User: Rolly Anand City: Delhi Company: Microsoft Salary: 3 Lakh

P.S: I think it is better to do it by Caml Query but don't know the exact way how to use it and Update that particular List Item.

Answer 1

Sample test demo for you reference:

public override void ItemAdded(SPItemEventProperties properties)
        {
            base.ItemAdded(properties);
            SPListItem item = properties.ListItem;
            using (SPWeb web = properties.OpenWeb())
            {
                SPQuery query = new SPQuery();
   string username = new SPFieldUserValue(web, item["User"].ToString()).User.Name;                
                query.Query = @"<Where>
      <And>
         <And>
            <Eq>
               <FieldRef Name='User' />
               <Value Type='User'>"+username+"</Value></Eq><Eq><FieldRef Name='City' /><Value Type='Choice'>" + item["City"] + "</Value></Eq></And> <Eq><FieldRef Name='Company' /><Value Type='Choice'>" + item["Company"] + "</Value> </Eq> </And></Where>";
                SPList list = web.Lists.TryGetList("listA");
                SPListItemCollection items = list.GetItems(query);
                if(items != null)
                {
                    foreach (SPListItem listitem in items)
                    {
                        listitem["Salary"] = "3 Lakh";
                        listitem.Update();
                    }
                }




            }

        }