Object_B__c has a field:
fieldobja__c (Type: Master-Detail)
Now, you get the error "Field is not writable" whenever you try to assign a value to the field "fieldobja__c" in either an Apex Class or a Trigger. Why??
This is because you can assign a value to this field only when you do an INSERT.
When you do an UPDATE, you CANNOT assign a value to this field.
In other words, you can assign a value only once.
Solution:
Assign a value only when the field has a value of NULL.
And this restriction does make sense, as this is a Master-Detail relationship.
Just took this solution from the above mentioned posts, summarizing below
Problem:
When a Visualforce Page loads, the date input field is selected by default. The usual behavior is that the first input field or box in the page is focussed by default. Clearly annoying in this case
Solution:
Add the below piece of code in your visualforce page.
<script>
function setFocusOnLoad() {}
</script>
Tried the other option suggested, but it does NOT work for me.
