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In cases like above, when you want to work only on a single entry, it is much easier to simply work on the associated directly.
For example, we could instead set the is a good fit.
Instead of setting the action manually, you may use .
This opens up the possibility to work on a subset of the data, instead of all associations in the database.
Imagine you are receiving a set of tags you want to associate to a post.
Let's imagine that those tags exist upfront and are all persisted to the database.
The difference between them is that most validations can be executed without a need to interact with the database and, therefore, are always executed before attempting to insert or update the entry in the database.
The first one is used to cast and validate external parameters, such as parameters sent through a form, API, command line, etc.If you need deletion, it is often preferred to add a separate boolean virtual field to the changeset function that will allow you to manually mark it for deletion, as in the example below: This means that when working with changesets that are not meant to be persisted to the database, such as schemaless changesets, you may need to explicitly set the action to one specific value.Frameworks such as Phoenix use the action value to define how HTML forms should act.For those reasons, changesets include the concept of empty values, which are values that will be automatically converted to the field's default value on See the documentation for those functions for more information.When using any of those APIs, you may run into situations where Ecto sees data is being replaced.