Use Bookshelf patch to set default values for unreferenced columns - node.js

Question

Here's my goal: Check if an entry exists in the postgres database. If the entry exists, update some of the columns in the entry with data I provide while setting unreferenced column values to null (or the default value). Otherwise just save a new entry.
I've been trying to understand what the patch argument actually does in bookshelf. It seems I can pass it with true or false and nothing changes in the behavior. From what I understand though it seems that passing it a false value should update all columns.
Let's say I have a table called table with columns user_id, timestamp, property1, property2. What I want to achieve with the below code should update the entry with the supplied values, but set property2 to the default value.
Models.table
.where({user_id: session.userId})
.fetch()
.then(tableEntry => {
let newTableEntry = {
user_id: session.userId,
timestamp: new Date(),
property1: "a string"
}
if (tableEntry){
return tableEntry.save(newTableEntry, {patch: false})
}
else {
return new Models.table().save(newTableEntry)
}
})
The only way I can seem to do this is explicitly set the other columns to null.

Answer 1

Why the patch option seems to make no difference
The reason you're not seeing any difference when using either true or false in the patch option is because you're already passing most of the attributes to update in the save call (user_id, timestamp and property1), and I assume that property2 already has a default value set in the database. So, patch will only update those 3 columns but since you're not passing the fourth one it will remain with its current value. If you don't use the patch option then the update query will use the value of property2 already set on the model which is the same as what's already on the database, therefore the patch option is almost useless in this case.
Patch's main difference is in the generated queries that are more efficient.
Updating an attribute with NULL
Now, if you explicitly pass an attribute value as null in the update statement it will set it to NULL in the database, but if you don't include that attribute then it won't be set:
tableEntry.save({timestamp: new Date(), property1: null}, {patch: true})
// UPDATE my_table SET timestamp = '2018...', property1 = NULL WHERE user_id = 1
tableEntry.save({timestamp: new Date()}, {patch: true})
// UPDATE my_table SET timestamp = '2018...' WHERE user_id = 1
Updating an attribute with a DEFAULT value
There's currently no support for that feature on Bookshelf. You can open a new feature request for that if you want.
However there's a similar feature that will allow you to use some default values in an update statement but you will have to provide these values yourself, without relying on the database to do it for you:
tableEntry.save({timestamp: new Date()}, {patch: true, defaults: true})
This requires that the model has an attribute with the default values:
var MyModel = bookshelf.Model.extend({
defaults: {property1: 'foo', property2: 'bar'},
tableName: 'my_table'
})
This feature isn't properly documented unfortunately, but it should work as intended.
When to use patch
This method is usually used when you fetch a model from the database like you did, but you're only interested in updating some of the attributes of the model. This is useful because by default Bookshelf will generate a query that will try to update all the attributes that are set on a model, not only those that are passed to save:
Models.table.forge({user_id: 1}).fetch().then(tableEntry => {
// tableEntry has all attributes set with a value
return tableEntry.save()
// This will generate a query like:
// UPDATE my_table SET user_id = 1, timestamp = '2018...',
// property1 = 'foo', property2 = 'bar', WHERE user_id = 1;
})
Using patch:
Models.table.forge({user_id: 1}).fetch().then(tableEntry => {
// tableEntry has all attributes set with a value
return tableEntry.save({property2: 'something'}, {patch: true})
// This will generate a query like:
// UPDATE my_table SET property2 = 'something', WHERE user_id = 1;
})