How to set up a multi field

Slider block in the MVC accelerator

For example, in the slider block in the MVC accelerator, we need to store an array of slides into a block's field. Each slide contains LinkText, ImagePointer and LinkToPage. 

Sample code performing the following actions:

1. Create a MultiField definition.
2. Create a group field template and link the MultiField to that template.
3. Create a static group and assign some values to the MultiField we have created in the first step.

public void Multi_Field_Group_Sample()
{
    //Create MultiField definition
    var multiFieldDefinition =
        new FieldDefinition<CustomerArea>(this.UniqueString(), SystemFieldTypeConstants.MultiField)
        {
            Option = new MultiFieldOption
            {
                IsArray = true,
                Fields = new List<string>
                {
                    SystemFieldDefinitionConstants.Name,
                    SystemFieldDefinitionConstants.Email,
                }
            }
        };
    _fieldDefinitionService.Create(multiFieldDefinition);

    //Create group field template and assign the MultiField definition to group
    var sampleGroupFieldTemplate = new GroupFieldTemplate(this.UniqueString())
    {
        FieldGroups = new[]
        {
            new FieldTemplateFieldGroup()
            {
                Id = "General",
                Collapsed = false,
                Fields =
                {
                    multiFieldDefinition.Id
                }
            }
        }
    };
    _fieldTemplateService.Create(sampleGroupFieldTemplate);

    //prepare multi field data 
    var innerData1 = new MultiFieldItem { AreaType = typeof(CustomerArea) };
    innerData1.Fields.AddOrUpdateValue(SystemFieldDefinitionConstants.Name, CultureInfo.CurrentCulture, "name1");
    innerData1.Fields.AddOrUpdateValue(SystemFieldDefinitionConstants.Email, "email1@domain.com");
    var innerData2 = new MultiFieldItem { AreaType = typeof(CustomerArea) };
    innerData2.Fields.AddOrUpdateValue(SystemFieldDefinitionConstants.Name, CultureInfo.CurrentCulture, "name2");
    innerData2.Fields.AddOrUpdateValue(SystemFieldDefinitionConstants.Email, "email2@domain.com");

    //Create a sample static group and assign multi field value to it:
    var sampleGroup = new StaticGroup(sampleGroupFieldTemplate.SystemId,this.UniqueString());
    sampleGroup.Fields.AddOrUpdateValue(multiFieldDefinition.Id,new [] {innerData1, innerData2});
    _groupService.Create(sampleGroup);

    //Retrieve the group we've created and extract the multifield value
    var savedGroup = _groupService.Get<StaticGroup>(sampleGroup.SystemId);
    savedGroup.Fields.TryGetValue(multiFieldDefinition.Id, out var multiFieldValue);

    //Retrieve values
    var list = IList<MultiFieldItem>(multiFieldValue);
    if(list != null)
    {
        var count = list.Count; // should be 2
        var name1 = list.First().Fields.GetValue<string>(SystemFieldDefinitionConstants.Name, CultureInfo.CurrentCulture); // should be "name1"
        var email1 = list.First().Fields.GetValue<string>(SystemFieldDefinitionConstants.Email) //Should be "email1@domain.com"
        var name2 = list.Last().Fields.GetValue<string>(SystemFieldDefinitionConstants.Name, CultureInfo.CurrentCulture); // should be "name2"
        var email2 = list.Last().Fields.GetValue<string>(SystemFieldDefinitionConstants.Email) //Should be "email2@domain.com"
    }
    
}

The MultiField data is stored in the same tables as normal fields (<EntityType>FieldData). Based on the ChildOwnerId and ChildIndex columns, we can group the individual values into objects. In the example below, we have three slides of the MultiField with the Id Slider. ChildIndex with the value 0 belongs to the first slide, and so on.

Custom validation

Implementations can create custom validation by implementing the IValidationRule interface. When validating MultiField nested fields, a custom validation rule must follow a specific convention for constructing the error ID. This ensures the system can correctly associate and display validation messages with the corresponding fields. The following example demonstrates this convention.:

[Service(Lifetime = DependencyLifetime.Scoped)]
internal class BaseProductRuleCustomForMultiField : ValidationRuleBase<BaseProduct>
{
    public override ValidationResult Validate(BaseProduct entity, ValidationMode validationMode)
    {
        var result = new ValidationResult();

        if (validationMode != ValidationMode.Remove)
        {
            var multifieldId = "multiField";
            var multiFieldItems = entity.Fields.GetValue<List<MultiFieldItem>>(multifieldId);
            
            // Iterate through each item in the multifield to apply validation.
            for (int i = 0; i < multiFieldItems.Count; i++)
            {
                // This is where your actual validation logic goes.
                // For instance, you could check if the "Color" field is empty.
                var validatedFieldId = "Color";
                // The key for the error message must follow this specific format:
                // {multiFieldId}_{baseProductSystemId}|{fieldId}|{index}
                // Note: The {index} starts at 1, so we use 'i + 1'
                result.AddError($"{multifieldId}_{entity.SystemId}|{validatedFieldId}|{i + 1}", $"Color is required");
            }

            // Use this line to add a general, non-specific error to the result.
            //result.AddError("*", "error message");
        }

        return result;
    }
}

For more information on validation, see: Object Validation.