Work with SharePoint Lookup Field Programmatically

In this article, we will explain How to Get and Set SharePoint Lookup Field Programmatically using C#?

You might also like to read Using Lookup Field in Calculated Column SharePoint

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SharePoint Lookup Field

In SharePoint List, you can create a column as a Lookup datatype that holds items from another list on the same site.

The Lookup columns (SPFieldLookup) can have multiple values or just single value based on the AllowMultipleValues property as shown below:

In case, the lookup column is a single value, the field value is an object of type SPFieldLookupValue with

• A 32-bit integer ID (LookupId) of the item in the list that the lookup field points to. 
• A string value (LookupValue) of the field in the item that the lookup field points to. 

In case, the lookup column allows multiple values, then the field value is an object of type SPFieldLookupValueCollection that is a collection of SPFieldLookupValue object.

Work with SharePoint Lookup Field Programmatically

So in this article, we will provide a complete Visual Studio Solution to learn How to Programmatically deal with Lookup field to to do the following:

1. Set a SharePoint Lookup Field (Single Value) using C#.
2. Set a SharePoint Lookup Field (Multiple Values) using C#.
3. Get a SharePoint SharePoint Lookup Field (Single Value) using C#.
4. Get a SharePoint SharePoint Lookup Field (Multiple Values) using C#.

You can download the complete solution from GitHub at SharePoint Lookup Field Operations In SSOM C#

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Get Lookup field SharePoint C# Programmatically

In this section, we we’ll learn how to get the Lookup Field Value (Single, Multiple) using C# as shown below:

Get SPLookup Field (Single Value) Using C#

The below code show How to get a SP Lookup field (Single Values) based on an existing item in a SharePoint List.

using(SPSite site = SPContext.Current.Site) {
  using(SPWeb web = site.OpenWeb()) {
    // Get The SPList
    SPList list = web.Lists["List Name"];
    // Get a list item By ItemID
    SPListItem item = list.GetItemById("A 32-bit integer that specifies the ID of List Item");
    //Get Lookup Field - Single Value
    SPFieldLookupValue SingleValue = new SPFieldLookupValue(item["The Lookup Field Name"].ToString());
    int SPLookupID = SingleValue.LookupId;
    string SPLookupValue = SingleValue.LookupValue;
  }
}

Get SPLookup Field (Multiple Values) Using C#

The below code shows How to get the SharePoint Lookup field (Multiple Values) based on an existing item in a SharePoint List and bind the retrieved data to a drop-down list.

using(SPSite site = SPContext.Current.Site) {
  using(SPWeb web = site.OpenWeb()) {
    // Get The SPList
    SPList list = web.Lists["LookupField"];
    // Get a list item By ItemID
    SPListItem item = list.GetItemById("A 32-bit integer that specifies the ID of List Item");
    //Get Lookup Field - Multiple Values
    SPFieldLookupValueCollection MultipleValues = item["The Lookup Field Name"] as SPFieldLookupValueCollection;
    foreach(SPFieldLookupValue itemValue in MultipleValues) {
      ListItem litem = new ListItem();
      litem.Text = itemValue.LookupValue;
      litem.Value = itemValue.LookupId.ToString();
      dropdownlist.Items.Add(litem);
    }
  }
}

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Set Lookup field SharePoint C# Programmatically

In this section, we we’ll learn how to update and set the Lookup Field Value (Single, Multiple) using C# as shown below:

Set SPLookup Field (Multiple Values) Using C#

The below code helps you to set the SharePoint Lookup field (Multiple Values) based on an existing item in a SharePoint List.

using(SPSite site = SPContext.Current.Site) {
  using(SPWeb web = site.OpenWeb()) {
    // Allow Unsafe Updates to prevent the cross site scripting
    web.AllowUnsafeUpdates = true;
    // Get The SPList
    SPList list = web.Lists["List Name"];
    // Add a new list item
    SPListItem item = list.Items.Add();
    // Set the default Title field
    item["Title"] = "string value";
    //Set Lookup Field - Multiple Values
    SPFieldLookupValueCollection itemValues = new SPFieldLookupValueCollection();
    foreach(ListItem litem in your collection) {
      itemValues.Add(new SPFieldLookupValue("A 32-bit integer that specifies the ID of the lookup field", "A string that contains the value of the lookup field"));
    }
    item["The Lookup Field Name"] = itemValues;

    // Submit your Item
    item.Update();
    web.AllowUnsafeUpdates = false;
  }
}

Set SPLookup Field (Single Value) Using C#

The below code show How to set SharePoint Lookup field (Single Values) based on an existing item in a SharePoint List.

using(SPSite site = SPContext.Current.Site) {
  using(SPWeb web = site.OpenWeb()) {
    // Allow Unsafe Updates to prevent the cross site scripting
    web.AllowUnsafeUpdates = true;
    // Get The SPList
    SPList list = web.Lists["List Name"];
    // Add a new list item
    SPListItem item = list.Items.Add();
    // Set the default Title field
    item["Title"] = "String Value";
    //Set the Lookup Field - Single Value
    item["The Lookup Field Name"] = new SPFieldLookupValue("A 32-bit integer that specifies the ID of the lookup field", "A string that contains the value of the lookup field");
    // Submit your Item
    item.Update();
    web.AllowUnsafeUpdates = false;
  }
}

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Conclusion

In conclusion, we have learned How to work with SharePoint Lookup Field Programmatically to to do the following:

1. Set a SharePoint Lookup Field (Single Value) using C#.
2. Set a SharePoint Lookup Field (Multiple Values) using C#.
3. Get a SharePoint SharePoint Lookup Field (Single Value) using C#.
4. Get a SharePoint SharePoint Lookup Field (Multiple Values) using C#.

Download

You can download the complete solution from

• GitHub: SharePoint Lookup Field Operations using SSOM C#.
• TechNet: SharePoint Lookup Field Operations In SSOM C#.

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• Retrieve a SharePoint Choice Field Value Using Server Object Model C#.

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