How to use Blob inside a Trigger (BLOB is not a valid UTF-8 string)?

Question

I am writing a trigger to Insert a Image in a record which will be posted via feed

string img;

trigger will save if I define "img" has a String on line 3 & "f.ContentData.tostring();" on line 7

If I tried to convert string to Blob it will say

Blob is not defined

    trigger Update_image on FeedItem (after insert) {
        id Travelid ;
        string img; 
     List<Object__c> lst = new List<Object__c>();

             For(FeedItem  f : Trigger.new){
                Travelid = f.parentid;
                 img = f.ContentData.tostring();
              }

    for(Object__c i :[select id,image__c from Object__c where id=: travelid]){
       i.image__c =img;
       lst.add(i);
    }
       update lst ;
}

In above trigger I am getting Error like this

System.StringException: BLOB is not a valid UTF-8 string

Answer 1

You have somehow embed the binary data into the field. Here's one way:

trigger Update_image on FeedItem (after insert) {
    id Travelid ;
    blob img; // Just binary data, thanks!
 List<Object__c> lst = new List<Object__c>();

         For(FeedItem  f : Trigger.new){
            Travelid = f.parentid;
             img = f.ContentData;
          }

for(Object__c i :[select id,image__c from Object__c where id=: travelid]){
   i.image__c = '<img src="data:image/jpeg;base64,'+EncodingUtil.base64Encode(img)+'"></img>';
   lst.add(i);
}
   update lst ;
}

Note that I've only copied/pasted your code (you may still have other issues here), but the idea is that you have to build an img tag yourself.

Edit:

So I just tried it, and salesforce automatically converts the image into a rtaImage file after saving. You can query the data back to see the changed image source. It'd be nice if this was clearly documented somewhere.

Answer 2

I was not able to convert Blob to String.. So I just Uploaded the Image to Document and Giving the Image URL in Rich Text Area Field

trigger Update_image on FeedItem (after insert) {

               id Travelid ;
               string Names;
               Blob body;  
               List<Object__c> lst = new List<Object__c>();

                     For(FeedItem  f : Trigger.new){
                            Travelid = f.parentid;
                          body=  f.contentdata;
                            Names= f.parentid;       
                      }

               Document d = new Document();
               d.name = Names;
               d.Body =  decodedbody;
               d.folderId= '00l90000000jkYA';
               insert d;  

            for(itravel__c i :[select id,image__c from Object__c where id=: travelid]){

                i.image__c ='<img src="https://c.ap1.content.force.com/servlet/servlet.FileDownload?file='+d.id+'" width="500" height="500"></img>';
               lst.add(i);
            }
               update lst ;

    }