Correctly convert DateTime property with Dapper on SQLite - datetime

Question

I'm using Dapper to insert and get objects to/from SQLite: one object have a property of type DateTime (and DateTimeOffset) that I have to persist and retrieve with milliseconds precision. I can't find a way to correctly retrieve the value because Dapper fail with:
System.FormatException : String was not recognized as a valid DateTime.
in System.DateTimeParse.ParseExactMultiple(String s, String[] formats, DateTimeFormatInfo dtfi, DateTimeStyles style)
in System.DateTime.ParseExact(String s, String[] formats, IFormatProvider provider, DateTimeStyles style)
in System.Data.SQLite.SQLiteConvert.ToDateTime(String dateText, SQLiteDateFormats format, DateTimeKind kind, String formatString)
in System.Data.SQLite.SQLite3.GetDateTime(SQLiteStatement stmt, Int32 index)
in System.Data.SQLite.SQLite3.GetValue(SQLiteStatement stmt, SQLiteConnectionFlags flags, Int32 index, SQLiteType typ)
in System.Data.SQLite.SQLiteDataReader.GetValue(Int32 i)
in System.Data.SQLite.SQLiteDataReader.GetValues(Object[] values)
in Dapper.SqlMapper.<>c__DisplayClass5d.<GetDapperRowDeserializer>b__5c(IDataReader r) in SqlMapper.cs: line 2587
in Dapper.SqlMapper.<QueryImpl>d__11`1.MoveNext() in SqlMapper.cs: line 1572
in System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
in System.Linq.Enumerable.ToList(IEnumerable`1 source)
in Dapper.SqlMapper.Query(IDbConnection cnn, String sql, Object param, IDbTransaction transaction, Boolean buffered, Nullable`1 commandTimeout, Nullable`1 commandType) in SqlMapper.cs: line 1443
in Dapper.SqlMapper.Query(IDbConnection cnn, String sql, Object param, IDbTransaction transaction, Boolean buffered, Nullable`1 commandTimeout, Nullable`1 commandType) in SqlMapper.cs: line 1382
What do I have to try? Column is of type DATETIME.
Do I have to create a custom TypeHandler and convert DateTime to and from a SQLite string in format "o"?
Dapper version 1.38

Answer 1

I know it's old, but I have found the solution.
After a lot of digging and analyzing Dapper code I came up with this (notice that this is 2019 year):
First you will have to create date time handler:
public class DateTimeHandler : SqlMapper.TypeHandler<DateTimeOffset>
{
private readonly TimeZoneInfo databaseTimeZone = TimeZoneInfo.Local;
public static readonly DateTimeHandler Default = new DateTimeHandler();
public DateTimeHandler()
{
}
public override DateTimeOffset Parse(object value)
{
DateTime storedDateTime;
if (value == null)
storedDateTime = DateTime.MinValue;
else
storedDateTime = (DateTime)value;
if (storedDateTime.ToUniversalTime() <= DateTimeOffset.MinValue.UtcDateTime)
return DateTimeOffset.MinValue;
else
return new DateTimeOffset(storedDateTime, databaseTimeZone.BaseUtcOffset);
}
public override void SetValue(IDbDataParameter parameter, DateTimeOffset value)
{
DateTime paramVal = value.ToOffset(this.databaseTimeZone.BaseUtcOffset).DateTime;
parameter.Value = paramVal;
}
}
Now, notice that Dapper translates .Net's type DateTimeOffset to dbType - DateTimeOffset. You need to remove this mapping and add your own like this:
SqlMapper.RemoveTypeMap(typeof(DateTimeOffset));
SqlMapper.AddTypeHandler(DateTimeHandler.Default);
That's all. Now everytime Dapper will see DateTimeOffset property in your model, it will run your DateTimeHandler to manage this.

Answer 2

I have found that custom TypeHandler for base types can't be used because of default typeMap that is choosen before looking for TypeHandler.
I have opened an issue dapper-dot-net but in the mean time I have solved replacing via reflection the default typeMap with a new one like the previous minus the four key DateTime, DateTime?, DateTimeOffset, DateTimeOffset?

Answer 3

I've made a slight modification to Adam Jachocki's solution as it didn't work for me. I am storing a date as TEXT in Sqlite and Dapper was giving me a string instead of a DateTime as the object value to parse. Apparently, Sqlite stores datetime values using three different data types: INTEGER (unix epoch), TEXT (ISO 8601 YYYY-MM-DD HH:MM:SS.SSS), and REAL ("number of days since noon in Greenwich on November 24, 4741 B.C."). That last one is really out there, so it isn't supported in the code below.
See the sqlite docs and this page for more info.
Below is my implementation of the DateTimeOffset TypeHandler. The rest of Adam's solution remains the same.
internal class DateTimeOffsetHandler : SqlMapper.TypeHandler<DateTimeOffset>
{
private static readonly TimeZoneInfo databaseTimeZone = TimeZoneInfo.Local;
private static readonly DateTime unixOrigin = new DateTime(1970, 1, 1, 0, 0, 0, 0);
public static DateTimeOffsetHandler Default { get; } = new DateTimeOffsetHandler();
public DateTimeOffsetHandler() {}
public override DateTimeOffset Parse(object value)
{
if (!TryGetDateTime(value, out DateTime storedDateValue))
{
throw new InvalidOperationException($"Unable to parse value {value} as DateTimeOffset");
}
if (storedDateValue.ToUniversalTime() <= DateTimeOffset.MinValue.UtcDateTime)
{
return DateTimeOffset.MinValue;
}
else
{
return new DateTimeOffset(storedDateValue, databaseTimeZone.BaseUtcOffset);
}
}
public override void SetValue(IDbDataParameter parameter, DateTimeOffset value)
{
DateTime paramVal = value.ToOffset(databaseTimeZone.BaseUtcOffset).DateTime;
parameter.Value = paramVal;
}
private bool TryGetDateTime(object value, out DateTime dateTimeValue)
{
dateTimeValue = default;
if (value is DateTime d)
{
dateTimeValue = d;
return true;
}
if (value is string v)
{
dateTimeValue = DateTime.Parse(v);
return true;
}
if (long.TryParse(value?.ToString() ?? string.Empty, out long l))
{
dateTimeValue = unixOrigin.AddSeconds(l);
return true;
}
if (float.TryParse(value?.ToString() ?? string.Empty, out float f))
{
throw new InvalidOperationException("Unsupported Sqlite datetime type, REAL.");
}
return false;
}
}