Djongo error when inserting record with foreign key in Django and MongoDB

Question

I am using django and mongodb as a database i have user model

class User(models.Model):
    userId = models.AutoField(primary_key=True)
    username = models.CharField(max_length=255)
    password = models.CharField(max_length=255)
    email = models.EmailField()
    phoneNo = models.CharField(max_length=15)

class Order(models.Model):
    WAITING = 'waiting'
    PROCESSING = 'processing'
    DELIVERED = 'delivered'

    STATUS_CHOICES = [
        (WAITING, 'Waiting'),
        (PROCESSING, 'Processing'),
        (DELIVERED, 'Delivered'),
    ]
    orderId = models.AutoField(primary_key=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    orderItems = models.IntegerField()
    orderTotalAmount = models.DecimalField(max_digits=10, decimal_places=2)
    status = models.CharField(max_length=20, choices=STATUS_CHOICES)

When I add a user, it is added successfully, but when I insert the record of the order, where username is the foriegn key, I am getting the following error:
djongo.exceptions.SQLDecodeError

Keyword: FAILED SQL: SELECT %(0)s AS "a" FROM "cafe_user" WHERE "cafe_user"."userId" = %(1)s LIMIT 1 Params: (1, 1) Version: 1.3.6 Sub SQL: None FAILED SQL: None Params: None Version: None

I am using djongo as a mongodb connector for django
I using mongodb first time can anyone know what the problem is? your text