How to create a asynchronous method in asp.net web API

Question

I need to get the data from my database using a web api. Below is the code on how I implement it.

[HttpGet]
[Authorize]
[Route("api/getproperties")]
public async Task<List<Property>> GetProperties()
{
    using(var db = new ApplicationDbContext())
    {
        var properties = await (from p in db.Properties
                        join pt in db.PropertyTypes
                        on p.PropertyTypeId equals pt.PropertyTypeId
                        select new
                        {
                            PropertyId = p.PropertyId,
                            PropertyName = p.PropertyName,
                            Owner = p.Owner,
                            Cluster = p.Cluster,
                            PropertyNumber = p.PropertyNumber,
                            RegionCode = p.RegionCode,
                            ProvinceCode = p.ProvinceCode,
                            MunicipalCode = p.MunicipalCode,
                            BarangayCode = p.BarangayCode,
                            DateAdded = p.DateAdded,
                            DateModified = p.DateModified,
                            PropertyTypeId = p.PropertyTypeId,
                            PropertyType = p.PropertyType,
                            Type = pt.Type
                        }
                                ).ToList()
                                .Select(x => new Property
                                {
                                    PropertyId = x.PropertyId,
                                    PropertyName = x.PropertyName,
                                    Owner = x.Owner,
                                    Cluster = x.Cluster,
                                    PropertyNumber = x.PropertyNumber,
                                    RegionCode = x.RegionCode,
                                    ProvinceCode = x.ProvinceCode,
                                    MunicipalCode = x.MunicipalCode,
                                    BarangayCode = x.BarangayCode,
                                    DateAdded = x.DateAdded,
                                    DateModified = x.DateModified,
                                    PropertyTypeId = x.PropertyTypeId,
                                    PropertyType = x.PropertyType,
                                    Type = x.Type
                                }).ToListAsync();

        return properties;
    }
}

If I do not use the "async Task>" and remove the ".ToListAsync()" and "await" at the beginning, I do not get the errors. But with it, the function is not going to be Asynchronous anymore. Can you please show me how to this right? Thank you.

Answer 1

When you use ToList() on IQueryable then asynchrony disappears since it loads data into memory synchronously.

Then you try to invoke ToListAsync on IEnumerable instead of IQueryable .

Your code should look like this:

public async Task<List<Property>> GetProperties()
{
    using(var db = new ApplicationDbContext())
    {
        var properties = await (from p in db.Properties
                          join pt in db.PropertyTypes
                          on p.PropertyTypeId equals pt.PropertyTypeId
                          select new Property()
                          {
                              PropertyId = p.PropertyId,
                              PropertyName = p.PropertyName,
                              Owner = p.Owner,
                              Cluster = p.Cluster,
                              PropertyNumber = p.PropertyNumber,
                              RegionCode = p.RegionCode,
                              ProvinceCode = p.ProvinceCode,
                              MunicipalCode = p.MunicipalCode,
                              BarangayCode = p.BarangayCode,
                              DateAdded = p.DateAdded,
                              DateModified = p.DateModified,
                              PropertyTypeId = p.PropertyTypeId,
                              PropertyType = p.PropertyType,
                              Type = pt.Type
                          }).ToListAsync();

        return properties;
    }
}