Asp.net API returns null for the columns related to other tables

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C#

API

I want to fetch data from database. My database has relational tables. Some of columns are linked to the ID of other tables.

In the output, I receive this:

[
    {
        "pmScheduleId": 28,
        "pmNumber": 100,
        "scheduledStartDate": "2022-06-22T00:00:00",
        "scheduledEndDate": "2022-07-05T00:00:00",
        "mainFileName": "2022-6-27-8972a000-7bc3-4013-b7bb-14d52f905970.xlsx",
        "uploadedFileName": null,
        "mainUploader": 1,
        "uploader": null,
        "completionDate": null,
        "status": "Registered",
        "costCenter": null,
        "serviceType": null
    },
    {
        "pmScheduleId": 29,
        "pmNumber": 130,
        "scheduledStartDate": "2022-06-22T00:00:00",
        "scheduledEndDate": "2022-07-05T00:00:00",
        "mainFileName": "2022-6-27-1dfb36b6-d348-4f6d-a8a1-ca2e585e713a.xlsx",
        "uploadedFileName": null,
        "mainUploader": 1,
        "uploader": null,
        "completionDate": null,
        "status": "Registered",
        "costCenter": null,
        "serviceType": null
    }
]

CostCenter and ServiceType needs to have values because they are filled with other table primary keys in the database. How can I fix this issue?

What I have tried:

I'm using the following code to fetch data from database:

public async Task<IActionResult> GetAllPmSchedules()
        {
            string userRole = HttpContext.Session.GetString("UserRole");
            if (userRole == "admin")
            {
                var pmSchedule = await _sqlServerContext.PmSchedules.ToListAsync();
                if (pmSchedule.Count > 0)
                {
                    return Ok(pmSchedule);
                }
                return NoContent();
            }
            return NotFound("Unauthorized access");
        }

My model is as follow:

public class PmSchedule
    {
        [Key]
        public long PmScheduleId { get; set; }
        [Required]
        public long PmNumber { get; set; }
        [Required]
        [DataType(DataType.DateTime)]
        public DateTime ScheduledStartDate { get; set; }
        [Required]
        [DataType(DataType.DateTime)]
        public DateTime ScheduledEndDate { get; set; }
        [Required]
        [DataType(DataType.Text)]
        public string MainFileName { get; set; }
        [DataType(DataType.Text)]
        public string? UploadedFileName { get; set; }
        [Required]
        public int MainUploader { get; set; }
        public int? Uploader { get; set; }
        [DataType(DataType.DateTime)]
        public DateTime? CompletionDate { get; set; }
        [Required]
        [DataType(DataType.Text)]
        public string? Status { get; set; }

        //Navigation properties
        public virtual CostCenter CostCenter { get; set; }
        public virtual ServiceType ServiceType { get; set; }
    }