Introducing The Gemli Project

by Jon Davis 23. August 2009 21:11

I’ve just open-sourced my latest pet project. This project was started at around the turn of the year, and its scope has been evolving over the last several months. I started out planning on a framework for rapid development and management of a certain type of web app, but the first hurdle as with anything was picking a favorite DAL methodology. I tend to lean towards O/RMs as I hate manually managed DAL code, but I didn’t want to license anything (it’d mean sublicensing if I redistribute what I produce), I have some issues with LINQ-to-SQL and LINQ-to-Entities, I find nHibernate difficult to swallow, I have some reservations about SubSonic, and I just don’t have time nor interest to keep perusing the many others. Overall, my biggest complaint with all the O/RM offerings, including Microsoft’s, is that they’re too serious. I wanted something lightweight that I don’t have to think about much when building apps.

So as a project in itself I decided first to roll my own O/RM, in my own ideal flavor. Introducing Gemli.Data! It’s a lightweight O/RM that infers as much as possible using reflection, assumes the most basic database storage scenarios, and helps me keep things as simple as possible.

That’s hype-speak to say that this is NOT a “serious O/RM”, it’s intended more for from-scratch prototype projects for those of us who begin with C# classes and want to persist them, and don’t want to fuss with the database too much.

I got the code functioning well enough (currently 92 unit tests, all passing) that I felt it was worth it to go ahead and let other people start playing with it. Here it is!

Gemli Project Home: 

Gemli Project Code:

Gemli.Data is currently primarily a reflection-based mapping solution. Here’s a tidbit sample of functioning Gemli.Data code (this comes from the CodePlex home page for the project):

// attributes only used where the schema is not inferred
// inferred: [DataModelTableMapping(Schema = "dbo", Table = "SamplePoco")]
public class SamplePoco
    // inferred: [DataModelFieldMapping(ColumnName = "ID", IsPrimaryKey = true, IsIdentity = true, 
    //     IsNullable = false, DataType = DbType.Int32)] // note: DbType.Int32 is SQL type: int
    public int ID { get; set; }

    // inferred: [DataModelFieldMapping(ColumnName = "SampleStringValue", IsNullable = true, 
    //     DataType = DbType.String)] // note: DbType.String is SQL type: nvarchar
    public string SampleStringValue { get; set; }

    // inferred: [DataModelFieldMapping(ColumnName = "SampleDecimalValue", IsNullable = true, 
    //     DataType = DbType.Decimal)] // note: DbType.Decimal is SQL type: money
    public decimal? SampleDecimalValue { get; set; }

public void CreateAndDeleteEntityTest()
    var sqlFactory = System.Data.SqlClient.SqlClientFactory.Instance;
    var dbProvider = new DbDataProvider(sqlFactory, TestSqlConnectionString);

    // create my poco
    var poco = new SamplePoco { SampleStringValue = "abc" };

    // wrap and auto-inspect my poco
    var dew = new DataModel<SamplePoco>(poco); // data entity wrapper

    // save my poco
    dew.DataProvider = dbProvider;
    dew.Save(); // auto-synchronizes ID
    // or...
    //dew.SynchronizeFields(SyncTo.ClrMembers); // manually sync ID

    // now let's load it and validate that it was saved
    var mySampleQuery = DataModel<SamplePoco>.NewQuery()
        .WhereProperty["ID"].IsEqualTo(poco.ID); // poco.ID was inferred as IsIdentity so we auto-returned it on Save()
    var data = dbProvider.LoadModel(mySampleQuery);
    Assert.IsNotNull(data); // success!

    // by the way, you can go back to the POCO type, too
    SamplePoco poco2 = data.Entity; // no typecast nor "as" statement
    Assert.IsTrue(poco2.ID > 0);
    Assert.IsTrue(poco2.SampleStringValue == "abc");

    // test passed, let's delete the test record
    data.MarkDeleted = true; 

    // ... and make sure that it has been deleted
    data = dbProvider.LoadModel(mySampleQuery);


Gemli.Data supports strongly typed collections and multiple records, too, of course.

var mySampleQuery = DataModel<SamplePoco>.NewQuery()
var models = dbProvider.LoadModels(mySampleQuery);
SamplePoco theFirstSamplePocoEntity = models.Unwrap<SamplePoco>()[0];
// or.. SamplePoco theFirstSamplePocoEntity = models[0].Entity;

Anyway, go to the URLs above to look at more of this. It will be continually evolving.

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About the author

Jon Davis (aka "stimpy77") has been a programmer, developer, and consultant for web and Windows software solutions professionally since 1997, with experience ranging from OS and hardware support to DHTML programming to IIS/ASP web apps to Java network programming to Visual Basic applications to C# desktop apps.
Software in all forms is also his sole hobby, whether playing PC games or tinkering with programming them. "I was playing Defender on the Commodore 64," he reminisces, "when I decided at the age of 12 or so that I want to be a computer programmer when I grow up."

Jon was previously employed as a senior .NET developer at a very well-known Internet services company whom you're more likely than not to have directly done business with. However, this blog and all of have no affiliation with, and are not representative of, his former employer in any way.

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