Web API giving exception in response

Question

Below is my web-api.

public HttpResponseMessage GetMeterPing(DateTime start, DateTime end)
{
    try
    {
        var startDateTime = start;
        var endDateTime = end;

        var result = medEntitites.tj_xhqd.Where(m => m.sjsj >= startDateTime && m.sjsj <= endDateTime)
                                         .OrderByDescending(o => o.sjsj)
                                         .Select(s => new { s.zdjh, s.sjsj, s.xhqd });
                                         .Distinct();
                                         
        return Request.CreateResponse(HttpStatusCode.OK, new { data = result });
    }
    catch (Exception ex)
    {
        return Request.CreateErrorResponse(HttpStatusCode.NotFound, ex);
    }
}

WEB-API UR:L http://localhost:14909/api/meters/GetMeterPing/2018-04-27T00:00:00/2018-04-28T23:59:59

When I run the above URL I am getting exceptions

{
"$id": "1",
"Message": "An error has occurred.",
"ExceptionMessage": "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.",
"ExceptionType": "System.InvalidOperationException",
"StackTrace": null,
"InnerException": {
    "$id": "2",
    "Message": "An error has occurred.",
    "ExceptionMessage": "An error occurred while reading from the store provider's data reader. See the inner exception for details.",
    "ExceptionType": "System.Data.Entity.Core.EntityCommandExecutionException",
    "StackTrace": "   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper`1.HandleReaderException(Exception e)\r\n   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper`1.StoreRead()\r\n   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper`1.SimpleEnumerator.MoveNext()\r\n   at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)\r\n   at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   at System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__1b.MoveNext()",
    "InnerException": {
        "$id": "3",
        "Message": "An error has occurred.",
        "ExceptionMessage": "Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.",
        "ExceptionType": "MySql.Data.MySqlClient.MySqlException",
        "StackTrace": "   at MySql.Data.MySqlClient.ExceptionInterceptor.Throw(Exception exception)\r\n   at MySql.Data.MySqlClient.MySqlConnection.Throw(Exception ex)\r\n   at MySql.Data.MySqlClient.MySqlConnection.HandleTimeoutOrThreadAbort(Exception ex)\r\n   at MySql.Data.MySqlClient.MySqlDataReader.Read()\r\n   at MySql.Data.Entity.EFMySqlDataReader.Read()\r\n   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper`1.StoreRead()",
        "InnerException": {
            "$id": "4",
            "Message": "An error has occurred.",
            "ExceptionMessage": "Timeout in IO operation",
            "ExceptionType": "System.TimeoutException",
            "StackTrace": "   at MySql.Data.MySqlClient.TimedStream.StopTimer()\r\n   at MySql.Data.MySqlClient.TimedStream.Read(Byte[] buffer, Int32 offset, Int32 count)\r\n   at System.IO.BufferedStream.Read(Byte[] array, Int32 offset, Int32 count)\r\n   at MySql.Data.MySqlClient.MySqlStream.ReadFully(Stream stream, Byte[] buffer, Int32 offset, Int32 count)\r\n   at MySql.Data.MySqlClient.MySqlStream.LoadPacket()\r\n   at MySql.Data.MySqlClient.MySqlStream.ReadPacket()\r\n   at MySql.Data.MySqlClient.NativeDriver.FetchDataRow(Int32 statementId, Int32 columns)\r\n   at MySql.Data.MySqlClient.Driver.FetchDataRow(Int32 statementId, Int32 columns)\r\n   at MySql.Data.MySqlClient.ResultSet.GetNextRow()\r\n   at MySql.Data.MySqlClient.ResultSet.NextRow(CommandBehavior behavior)\r\n   at MySql.Data.MySqlClient.MySqlDataReader.Read()"
        }
    }
}
}

WebApiConfig

var json = config.Formatters.JsonFormatter;
        json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
        config.Formatters.Remove(config.Formatters.XmlFormatter);

Application_Start()

GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings
.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
        GlobalConfiguration.Configuration.Formatters
            .Remove(GlobalConfiguration.Configuration.Formatters.XmlFormatter);

I have also looked into these solutions 1, 2 But it still gives me exceptions.

Also, I have tried with .ToList() but unable to get desired results.

Note: I am using MySQL Database

Update 1:

 var result = medEntitites.tj_xhqd.Where(m => m.sjsj >= startDateTime && m.sjsj <= endDateTime)
                                             .OrderByDescending(o => o.sjsj)
                                             .Select(s => new { s.zdjh, s.sjsj, s.xhqd })
                                             .Distinct()
                                             .FirstOrDefault();    

By using FirsOrDefault() I am getting a single row returned

{
"data": {
    "zdjh": "002999001089",
    "sjsj": "2018-04-27T00:00:00",
    "xhqd": "19"
}
}

But I want API to return all the records between the date time given

How can I get rid of these exceptions?

Any help would be highly appreciated.