context.ToListAsync() 没有从表中获取任何数据

Question

The table was created before I created the DBSet for "AssetResource". Since I want to use the EF to make it easier to insert or update, I created the DbSet<AssetResource> without calling the add-migration. The table has some data in it already, but when I call using this

var list = await context.AssetSources.ToListAsync();

I get an error of Data is Null then goes to the Exception.

I tried adding the migration and creates it successfully but when I command the update-database , it tells me that the Resources table is already existing which is actually right because this table has been created before I created the DbSet<AssetResource> .

Here's the whole code of getting the list:

public async Task<IEnumerable<AssetSource>> GetAssetResources()
        {
            var lAssetSource = new List<AssetSource>();
            try
            {
                var sw = new Stopwatch();
                if (cache.TryGetValue(CACHE_KEYASSETSOURCE, out List<AssetSource> refListAssetSource))
                {
                    helper.LogMessage("Assets Sources are found in cache", LoggerModel.LoggingType.Information);
                    lAssetSource = refListAssetSource;
                }
                else
                {
                    var l = await context.AssetSources.ToListAsync();
                }
                return lAssetSource;
            }
            catch (Exception e)
            {
                helper.LogMessage(e.Message, Shared.Models.LoggerModel.LoggingType.Error);
                throw new NoObjectDetectedException(e.Message);
            }
        }

Answer 1

Data is null means that entity framework tries to bind nullable db column to non nullable property. Make sure that if the db column is for example int, null that the entity model in c# is int? and not int .

Answer 2

Manually delete the table and then run the update-database command and you should be good. If you delete the table there will be no data in the table when running the update-database command. A good idea would be to rename the existing table before running the command, so you still have the existing data in the renamed table.