Use Dapper to hydrate complex object

Question

I did some digging into this, but I don't quite understand it. I have a Microsoft.Extensions.Logging.EventId on an object and I've used Dapper to preserve the EventId in my database. I used two columns: EventId (int) and EventName (varchar(…)). However, I can't quite figure out how to populate the one property object (EventId) from the two database columns.

I tried manipulating my SQL . .

SELECT <snip>…[EventId] AS [EventId.Id],[EventName] AS [EventId.Name] . . .

but that worked about as you might expect.

So, here's my xunit test:

[Fact]
public async Task EventName_Retrievable()
{
    logger.Log(logLevel: LogLevel.Critical,
        eventId: new EventId(10, "find me"),
        exception: null,
        state: "yes please",
        formatter: (s, e) =>
        {
            return e?.Message ?? s;
        });

    var criteria = new LogQueryCriteria
    {
        MessageContains = "yes please"
    };
    var service = new LogQueryService(_fixture.ConnectionString, _factory, _performanceAgent);

    var logs = await service.FindLogsAsync(criteria);

    Assert.NotEmpty(logs);

    Assert.Equal("find me", logs.Last().EventId.Name);
}

which proves that this function doesn't work:

    public async Task<IEnumerable<ILogItemOutbound>> FindLogsAsync(LogQueryCriteria criteria)
    {
        var pe = _performanceAgent?.Start($"{nameof(LogQueryService)}.{nameof(FindLogsAsync)}", PerformanceTrackingLevel.Low);

        if (criteria == null) { criteria = new LogQueryCriteria(); }

        IEnumerable<ILogItemOutbound> results = null;
        var sql = $@"
{Constants.SELECT_LOGS}{ConstructWhereClause(criteria)} {ConstructOrderByClause(criteria)}
OFFSET {criteria.OffsetValue} ROWS FETCH NEXT {criteria.NumberPerPage} ROWS ONLY;";

        using (var connection = new SqlConnection(_connectionString))
        {
            connection.Open();
            results = await connection.QueryAsync<LogItemOutbound, EventId, LogItemOutbound>(sql: sql, commandType: System.Data.CommandType.Text,
                map: (logItem, eventId) =>
                {
                    logItem.EventId = eventId;
                    return logItem;
                }
            , splitOn: "EventId");
            _performanceAgent?.Finish(pe);
        }

        return results ?? new List<ILogItemOutbound>();
    }

You can see that I attempted to use the map function sort of like this person did: https://taylorhutchison.github.io/2016/03/23/dapper-orm-complex-queries.html, but the Name always turns up NULL, regardless of my approach.

Anyone see where I'm going wrong?

If relevant, here is my SQL:

    internal const string SELECT_LOGS = @"
SET NOCOUNT ON;
SET DEADLOCK_PRIORITY NORMAL;

SELECT [GlobalId]
,[UtcTimestamp]
,[Message]
,[LogLevel]
,[LogLevelName]
,[Source]
,[UserIdentity]
,[SessionId]
,[EventId]
,[EventName]
FROM [dbo].[Logs]";

Help is always appreciated.

V

Richard Hubley · Accepted Answer · 2018-08-27 18:28:24Z

1

EventName will not map to Event.Name

Change your SQL to

 internal const string SELECT_LOGS = @"
SET NOCOUNT ON;
SET DEADLOCK_PRIORITY NORMAL;

SELECT [GlobalId]
,[UtcTimestamp]
,[Message]
,[LogLevel]
,[LogLevelName]
,[Source]
,[UserIdentity]
,[SessionId]
,[EventId] as Id
,[EventName] as Name
FROM [dbo].[Logs]";

and your spliton: "Id"

answered Aug 27, 2018 at 18:28

Richard Hubley

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