Recently, I refactored some code which resulted in changing the type of some properties of an entity from System.String
to System.URI
. The names of the properties in question contained the substring URI or URL and the SonarLint static code analyzer was recommending that the code be refactored to use the System.URI
type instead of System.String
for those properties, which makes sense in our solution.
In this project, we are leveraging StackExchange's Dapper as an ultra fast and light object mapper, but after the refactoring, I started receiving this error when trying to retrieve data from my repository:
System.Data.DataException
HResult=0x80131501
Message=Error parsing column 5 (RequestUrl=https://www.myurl.com/api/wow - String)
Source=Dapper
StackTrace:
at Dapper.SqlMapper.ThrowDataException(Exception ex, Int32 index, IDataReader reader, Object value) in C:\projects\dapper\Dapper\SqlMapper.cs:line 3609
at Dapper.SqlMapper.<>c__DisplayClass156_0`8.<GenerateMapper>b__1(IDataReader r) in C:\projects\dapper\Dapper\SqlMapper.cs:line 1544
at Dapper.SqlMapper.<MultiMapImpl>d__153`8.MoveNext() in C:\projects\dapper\Dapper\SqlMapper.cs:line 1444
at System.Collections.Generic.List`1.AddEnumerable(IEnumerable`1 enumerable)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at Dapper.SqlMapper.<MultiMapAsync>d__52`8.MoveNext() in C:\projects\dapper\Dapper\SqlMapper.Async.cs:line 949
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
at My.Namespace.MyRepository.<GetAllRepositoryMethod>d__2.MoveNext() in C:\dev\repos\myproject\MyRepository.cs:line 59
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at My.Namespace.Program.CallerMethod(Object sender, ElapsedEventArgs e) in C:\dev\repos\myproject\Program.cs:line 109
at System.Timers.Timer.MyTimerCallback(Object state)
Inner Exception 1:
InvalidCastException: Invalid cast from 'System.String' to 'System.Uri'.
How can I get around this error?
It turns out that Dapper is easily extensible and by declaring a simple class that extends SqlMapper.TypeHandler<T>
, you can define a mapping (TypeHandler) between the System.String
and System.URI
types and enable Dapper to perform the cast.
Here's what that class looks like:
using System;
using System.Data;
using Dapper;
namespace My.Namespace.Data.DatabaseTools
{
public class DapperUriTypeHandler : SqlMapper.TypeHandler<Uri>
{
public override void SetValue(IDbDataParameter parameter, Uri value)
{
parameter.Value = value.ToString();
}
public override Uri Parse(object value)
{
return new Uri((string)value);
}
}
}
Once you have declared the mapping, you can let Dapper know about it by calling the SqlMapper.AddTypeHandler
method and providing an instance of your custom type handler class as a parameter like so:
SqlMapper.AddTypeHandler(new DapperUriTypeHandler());
The best place to call SqlMapper.AddTypeHandler
is somewhere in your startup configuration so that the type handler is known to Dapper early on in the execution of your application or service.
I Hope this can help other community members resolve similar issues with Dapper and type casting quickly in the future!
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