dpoineau / jell

A Dapper-like JDBC wrapper library.

jell

Jell is a micro-ORM for Java. It allows you to easily execute SQL in Java, as well as automatically mapping parameters from an object and query results back to a specific class. If you don't specify a class, it will map to a dynamic object.

Maven

You can get Jell from Maven Central.

<dependency>
    <groupId>com.noelherrick</groupId>
    <artifactId>jell</artifactId>
    <version>0.1.1</version>
</dependency>

Examples

Creating a jell instance

A new Jell instance is created by passing in a JDBC connection.

Connection conn = DriverManager.getConnection(url, username, password);

Jell jell = new Jell(conn);

Querying

ParamClass is a simple POJO with the fields "number" and "string".

ParamClass param = new ParamClass("a", 2);

String sql = "select 1 as number, 'b' as str where 'a' = @string and 2 = @number";

Collection<ParamClass> results = jell.query(sql, ParamClass.class, param);

Executing

If you have a simple SQL statement, executing is simple:

jell.execute("create table basic_post (id int primary key, title varchar(50) not null)");

Batch inserts

If you have a bunch of inserts, this is simple as well.

List<ParamClass> pojos = new ArrayList<>();

for (int i = 0; i < 1_000_000; i++)
{
    pojos.add(new ParamClass("a", i));
}

jell.executeBatch("insert into basic_post values (@number, @string)", pojos);

Hashes

I wanted something similar to dynamic objects in .NET, but Java does not help me here, so if you don't specify a class to map query results to, it will give you a map-like object.

Collection<Dyno> dynos1 = jell.query("select * from basic_post limit 10", false);

for (Dyno dyno : dynos1) {
    System.out.println(dyno.str("title"));
}

The origin

Whenever I start a .NET project that uses the database, I will almost always fall back to Dapper. It reduces the friction of using an RDBMS in C# code. The standard ADO.NET (.NET's JDBC) API is verbose and painful. With Dapper, I only need to create an ADO.NET connection and I can start writing SQL. Queries are automatically to the class or primitive you specify. Dapper is incredibly near the speed of using ADO.NET, so I choose it over other ORM's.

I wanted something similar for Java, so I built this.

Limitations

Java has several limitations that preclude me from writing a full Dapper replacement in the language.

1. Java does not have reified generics (or type filters). I must do some reflection magic and hope it works. Unlike C#, I cannot guarantee at compile time that your passed-in class has a parameter-less constructor.
2. Java lacks the dynamic object. This disallows both dynamic parameter objects and dynamic result objects. I most often use the former.
3. Java has no viable replacement for extension methods. This means we have to create a separate object using the connection, instead of using a static method like Dapper does.

The name

So you know the .NET library, Dapper. Well, what makes you dapper, at least in the 90s and the 00s? Gel, of course! And since it's a Java library, it's jell!