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How to use preImage and postImage in Plugins

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Posted on by Joel D

363

I created a Plugin which is triggered while updating a Movie and shows an error when the fields "Title" and "Year" are left empty.

I also need to use PreImage to check whether the value is present in the pre-image but not in the target, i.e. if it was erased by the user.

I wrote the following code, but it doesn't work, can you please tell me if I'm using preImage and PostImage correctly?

public void Execute(IServiceProvider serviceProvider)
        {
            var context = new PluginContext(serviceProvider);
            var service = context.CrmServiceSystem;
            var trace = context.TracingService;
            var target = context.GetTarget();

            var preImage = context.GetPreImage();
            if (target == null)
                return;
            var postImage = preImage.Merge(target);
            
            // case 1: the field is left empty and it was empty before too: 

            if((!preImage.Attributes.Contains("title") && !postImage.Attributes.Contains("title"))
                ||
                
                // case 2: the field was not empty, but the user deleted the content:
                (preImage.Attributes.Contains("title") && !postImage.Attributes.Contains("title")))
            {
                throw new InvalidPluginExecutionException(OperationStatus.Failed, "Title can't be null");
            }

            if ((!preImage.Attributes.Contains("year") && !postImage.Attributes.Contains("year"))
                ||
                (preImage.Attributes.Contains("year") && !postImage.Attributes.Contains("year")))
            {
                throw new InvalidPluginExecutionException(OperationStatus.Failed, "Year is null!");
            }
           
        }

For instance, I have this issue: when the Year is already correct and I don't modify it, I get the error "Year can't be null". As I merged the PreImage with the target, why the value is not recognized?

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Community Member on at

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Here is how I have seen it used in plugins before:

Entity preImage = (Entity)context.PreEntityImages["Image"];

If not this, can you add any tracing just after you set the preImage variable to see whats in it?

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Guido Preite 54,086 Moderator on at

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for the requirement you wrote (shows an error when the fields "Title" and "Year" are left empty) you just need to trigger your plugin as post sync on both fields and use a single post image containing these two fields.

in your plugin you get the fields from the post image and if one of them is empty then you show the error.

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Joel D 363 on at

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Thank you for replying.
@Guido I wrote the following, is it correct? How can I trigger the plugin as post sync, do you mean that I should register it as post-operation?

var targetEntity = context.GetTarget(); var preImage = context.GetPreImage(); if (targetEntity == null) return; var postImage = preImage.Merge(target); if (!postImage.Contains("title")) throw new InvalidPluginExecutionException(OperationStatus.Failed, "Title is empty!"); if (!postImage.Contains("year")) throw new InvalidPluginExecutionException(OperationStatus.Failed, "Year is empty!");

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Guido Preite 54,086 Moderator on at

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how the plugin is executed (pre, post, async, sync) and the registration of images (pre, post) and their attributes is done entirely with Plugin Registration Tool (by the executable from nuget or using the one inside XrmToolBox)

in your code I don't think it's necessary that Merge operation that you are doing (because I don't know how it will merge the attributes) but if you are in a post sync, the attributes on the image will be the same as the attributes of the target/current entity.

also in your check I would avoid the use of Contains, Contains returns if the attribute is present inside the collection of attributes or not (and you can have a case where the attribute is there but is null for example)

I would use the GetAttributeValue, something like this

string year = postImage.GetAttributeValue<string>("year");

if (String.IsNullOrWhiteSpace(year)) { throw new InvalidPluginExecutionException(OperationStatus.Failed, "Year is empty!"); }

in my code I assumed that year is a string, if is a whole number you should use an int?

int? year = postImage.GetAttributeValue<int?>("year");

if (!year.HasValue) { throw new InvalidPluginExecutionException(OperationStatus.Failed, "Year is empty!"); }

to summarize:

1) just use a post image with just these two attributes

2) use GetAttributeValue instead of Contains to check if the value is actually null

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Joel D 363 on at

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Thanks.

What if I wanted to do the same with a lookup field, e.g I want to check the filed "Director" which is a lookup named "director_id" ?

I defined the variable as in the following:

EntityReference director= postImage.GetAttributeValue("director_id");

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Guido Preite 54,086 Moderator on at

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EntityReference is null when is not set, when is set means is filled

if (director == null) { /* lookup is empty */} else { /* lookup has value */ }

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Joel D 363 on at

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I checked whether the lookup is empry but the plugin does not work for the director field: when I don't edit the text inside it throws the exception.

My updated code is the following:

EntityReference director = postImage.GetAttributeValue<EntityReference>("director");
if (director == null)
throw new InvalidPluginExecutionException(OperationStatus.Failed, "Director is empty!");

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Guido Preite 54,086 Moderator on at

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you need to make sure that this director field is inside the postimage, otherwise you can't get the correct value from it

more than this I can't suggest as I don't have access to your instance, so if there are other parts of your code that may interfere with this logic

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