README_UPDATE.md

Update

Update(...) requires the resource to be updated with its fields set that the caller wants updated.

A fieldMask is optional and provides paths for fields that should be updated.

A setToNullPaths is optional and provides paths for the fields that should be set to null.

Either a fieldMaskPaths or setToNullPaths must be provided and they must not intersect.

The caller is responsible for the transaction life cycle of the writer and if an error is returned the caller must decide what to do with the transaction, which almost always should be to rollback. Update returns the number of rows updated.

There a lots of supported options: WithBeforeWrite, WithAfterWrite, WithWhere, WithDebug, and WithVersion.

If WithVersion is used, then the update will include the version number in the update where clause, which basically makes the update use optimistic locking and the update will only succeed if the existing rows version matches the WithVersion option. Zero is not a valid value for the WithVersion option and will return an error.

WithWhere allows specifying an additional constraint on the operation in addition to the PKs.

WithDebug will turn on debugging for the update call.

Simple update WithVersion example

user.Name = "Alice"
rowsAffected, err = rw.Update(ctx, 
    &user, 
    []string{"Name"}, 
    nil, 
    dbw.WithVersion(&user.Version))

Update with setToNullPaths and WithVersion example

user.Name = "Alice"
rowsAffected, err = rw.Update(ctx, 
    &user, 
    nil, 
    []string{"Name"}, 
    dbw.WithVersion(&user.Version))