I have a filter that has a SelectInput inside a ReferenceInput and it has only one option. I really need that first option to be selected.
<ReferenceInput source="BranchID" reference="branches" allowEmpty alwaysOn perPage={1000}>
<SelectInput optionText={choice => `${choice.number +" "+ choice.address}`} />
</ReferenceInput>
You can achieve that using default values on your form: https://marmelab.com/admin-on-rest/CreateEdit.html#default-values