Content Items event handler: how to intercept the saving event of a Content Item?

[MarGraz]

Hi everyone,

I'm trying to understand if there's the possibility of using an event handler to intercept when a Content Item, created in the backoffice, is saved by the admin. I know there's the possibility to use ContentPartHandler<TPart> and ContentFieldHandler<TField>, as well explained in this video. But how about Content Items?

I need to intercept the saving of a Book Content Item, to perform some checks on a BagPart contained within the Book. How can I intercept the Content Item saving event?

I imagine something like this:

using OrchardCore.ContentManagement.Handlers;
using OrchardCore.ContentManagement;
using System.Threading.Tasks;

public class CustomContentItemHandler : ContentHandler
{
    public override async Task UpdatingAsync(UpdateContentContext context)
    {
        var contentItem = context.ContentItem;

        // Intercept Book Content Item
        if (contentItem.ContentType == "Book")
        {
            // Retrieve here the "Bag" part contained in it, and perform checks
        }

        await base.UpdatingAsync(context);
    }
}

1. Of course, a ContentHandler like this one doesn't exist, but is that possible, or am I dreaming? 😁
2. Or is there a way to intercept the save event for a non-custom ContentPart or ContentField, such as the BagPart, already available in Orchard Core, and contained in a specific Content Item?

Thank you

[douwinga]

You are looking for ContentHandlerBase. Personally, unless this content type is created via a migration in code and also has an associated BookPart with model in the same module, I would just handle something like this in a workflow using the Content Updated event. And if you had a BookPart you would use the ContentPartHandler anyways. Targeting a specific content type in a ContentHandlerBase just feels like the wrong tool to me.

[douwinga]

I think I missed your second question. Yes you can have event handlers on existing parts such as BagPart. Just do the same thing you would for a custom part public class MyBagPartHandler : ContentPartHandler<BagPart> and then in the startup services.AddContentPart<BagPart>().AddHandler<MyBagPartHandler>();. It may seem odd to be calling AddContentPart on a Part that has already been added, but if you look, this method calls GetOrAddContentPart, so you are not adding it twice.

Now that I think I understand what you are trying to do, this is probably the best approach and you can ignore the workflow idea. ContentPartHandlers can get the content item easily enough, so for some reason if you had to do a check for the content type of Book you could still do that.

[MarGraz]

@douwinga thank you for your reply, as always 😊

Essentially, I need to intercept the saving of a Book - a content item created from the backoffice UI, not a custom one -. I need to take the BagPart within it, and checking the number of items in the BagPart against the Min and Max values - we discussed it here -. If the items do not meet these criteria, I want to send an error message back to the admin.

I will try using the ContentPartHandler approach. Let's see how it turns out.

Thank you

[MarGraz]

@douwinga it works 🥳
I also added a check on the Content Type Book, because this BagPart handler is called every time a Content Item has a BagPart in it.

I'm not sure if I need to add a null check on Result property, in var partDefinition = contentTypeDefinition.Result{here}.
This is an example of what I have implemented:

using CodingOps.Custom.ContentFields.Models;
using OrchardCore.ContentManagement.Handlers;
using OrchardCore.ContentManagement.Metadata;
using OrchardCore.Flows.Models;

public class BookBagPartHandler : ContentPartHandler<BagPart>
{
    // ContentDefinitionManager is necessary to retrieve the custom settings
    // ("max" and "min" values) I have added to every BagPart.
    // See this discussion: https://github.com/OrchardCMS/OrchardCore/discussions/15549#discussioncomment-8845326
    private readonly IContentDefinitionManager _contentDefinitionManager;

    public BookBagPartHandler(IContentDefinitionManager contentDefinitionManager)
    {
        _contentDefinitionManager = contentDefinitionManager;
    }

    public override async Task UpdatingAsync(UpdateContentContext context, BagPart part)
    {
        // Check if the type of the BagPart is a Book Content Item
        if (context.ContentItem.ContentType == "Book")
        {
            // Retrieve the settings
            var contentTypeDefinition = _contentDefinitionManager.GetTypeDefinitionAsync("Book");
            var partDefinition = contentTypeDefinition.Result.Parts.FirstOrDefault(p => p.PartDefinition.Name == nameof(BagPart));
            var settings = partDefinition.GetSettings<CustomBagPartSettings>();

            int minItems = settings.MinItems;
            int maxItems = settings.MaxItems;

            // Now I can use minItems and maxItems as needed
            int itemCount = part.ContentItems.Count;
            if (itemCount < minItems || itemCount > maxItems)
            {
                // Perform my validation or other logic here
            }
        }

        await Task.CompletedTask;
    }
}

Thank you

[douwinga]

typically you would use await instead of using .Result because a) it is cleaner looking code and b) .Result can end up causing deadlocks. Something like this:

public override async Task UpdatedAsync(UpdateContentContext context, BagPart part)
{
    // Check if the type of the BagPart is a Book Content Item
    if (context.ContentItem.ContentType != "Book")
    {
        return;
    }

    // Retrieve the settings
    var contentTypeDefinition = await _contentDefinitionManager.GetTypeDefinitionAsync("Book");
    var partDefinition = contentTypeDefinition?.Parts?.FirstOrDefault(p => p.PartDefinition.Name == nameof(BagPart));
    var settings = partDefinition?.GetSettings<CustomBagPartSettings>();

    if (settings == null)
    {
        return;
    }

    int minItems = settings.MinItems;
    int maxItems = settings.MaxItems;

    // Now I can use minItems and maxItems as needed
    int itemCount = part.ContentItems.Count;
    if (itemCount < minItems || itemCount > maxItems)
    {
        // Perform my validation or other logic here
    }
}

[MarGraz]

@douwinga in my previous comment I changed the UpdatedAsync method in UpdatingAsync, because I need to perform the validation before the saving.

I saw that there's no context.fail() method for the UpdateContentContext type. How can I return an error message to the backoffice UI in case the validation fails?

Thank you