Booking system - Availabilty check with Ajax to database

I am very new to MVC and I am trying to create a booking system in MVC5. I have set up a my database by EF code first. My booking table is:
     

     public class Booking
    {
       [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid BookingId { get; set; }

        [ForeignKey("Patient")]
        public Guid PatientId { get; set; }
        public virtual Patient Patient { get; set; }
        public IEnumerable<SelectListItem> PatientList { get; set; }

        [ForeignKey("Practice")]
        public Guid PracticeId { get; set; }
        public virtual Practice Practice { get; set; }
        public IEnumerable<SelectListItem> PracticeList { get; set; }

        [ForeignKey("Optician")]
        public Guid OpticianId { get; set; }
        public virtual Optician Optician { get; set; }
        public IEnumerable<SelectListItem> OpticiansList { get; set; }

        [Display(Name = "Date")]
        [DataType(DataType.Date)]
        [DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:dd/MM/yyyy}")]
        public DateTime Date { get; set; }

        [ForeignKey("Time")]
        public Guid? TimeId { get; set; }
        public virtual Time Time { get; set; }
        public IEnumerable<SelectListItem> TimeList { get; set; }
        
        public bool isAvail { get; set; }
    }

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I have used CRUD to make a Create page. Once a booking has been made the isAvail boolean is set to False.
What I am trying to do is create an AJAX query so that once the user selects the practice, optician and date the ajax query checks the database to see if the combination of practice, optician and date does not exist alongside isAvail - false in order to prevent double bookings. The ajax query would then return the available times ie - the time where there is no isAvail = false.

Any help would be greatly appreciated
Thanks