Table of Contents

KEFCore: Getting started

To use Entity Framework Core provider for Apache Kafka you must have at least:

  • an installed JRE/JDK (11+)
  • an accessible Apache Kafka broker (a full cluster or a local Dockerized version)

IMPORTANT NOTE: till the first major version, all releases shall be considered not stable: this means the API public, or internal, can change without notice.

First project setup

  • Create a new simple empty project:
dotnet new console
  • Entity Framework Core provider for Apache Kafka is available on NuGet. Execute the following command to add the package to the newly created project:
dotnet add package MASES.EntityFrameworkCore.KNet
  • Edit Program.cs and replace the content with the following code:
using MASES.EntityFrameworkCore.KNet.Infrastructure;
using System.Collections.Generic;

namespace MASES.EntityFrameworkCore.KNet.Test
    class Program
        static void Main(string[] args)
            using var context = new BloggingContext()
                BootstrapServers = "MY-KAFKA-BROKER:9092",
                ApplicationId = "MyAppId",
                DbName = "MyDBName",
            // add standard EFCore queries

    public class BloggingContext : KafkaDbContext { }

    public class Blog
        public int BlogId { get; set; }
        public string Url { get; set; }
        public int Rating { get; set; }
        public List<Post> Posts { get; set; }

    public class Post
        public int PostId { get; set; }
        public string Title { get; set; }
        public string Content { get; set; }

        public int BlogId { get; set; }
        public Blog Blog { get; set; }

The previous code follows the example of See KEFCore usage and KafkaDbContext to find more information.

  • Build the project
dotnet build

Environment initialization

KEFCore shall initialize the environment before any operation can be done. The initialization is done executing the following command at first stages of your application:


The previous command identify the JVM and start it, loads the needed libraries and setup the environment. Browsing the repository within the test folder there are some examples. KEFCore accepts many command-line switches to customize its behavior, the full list is available at Command line switch of KNet.

JVM identification

One of the most important command-line switch is JVMPath and it is available in JCOBridge switches: it can be used to set-up the location of the JVM library if JCOBridge is not able to identify a suitable JRE/JDK installation. If a developer is using KEFCore within its own product it is possible to override the JVMPath property with a snippet like the following one:

    class MyKEFCore : KEFCore
        public override string JVMPath
                string pathToJVM = "Set here the path to JVM library or use your own search method";
                return pathToJVM;

IMPORTANT NOTE: pathToJVM shall be escaped

  1. string pathToJVM = "C:\\Program Files\\Eclipse Adoptium\\jdk-\\bin\\server\\jvm.dll";
  2. string pathToJVM = @"C:\Program Files\Eclipse Adoptium\jdk-\bin\server\jvm.dll";

Special initialization conditions

JCOBridge try to identify a suitable JRE/JDK installation within the system using some standard mechanism of JRE/JDK: JAVA_HOME environment variable or Windows registry if available. However it is possible, on Windows operating systems, that the library raises an InvalidOperationException: Missing Java Key in registry: Couldn't find Java installed on the machine. This means that neither JAVA_HOME nor Windows registry contains information about a default installed JRE/JDK: some vendors may not setup them. If the developer/user encounter this condition can do the following steps:

  1. On a command prompt execute set | findstr JAVA_HOME and verify the result;
  2. If something was reported maybe the JAVA_HOME environment variable is not set at system level, but at a different level like user level which is not visible from the KEFCore process that raised the exception;
  3. Try to set JAVA_HOME at system level e.g. JAVA_HOME=C:\Program Files\Eclipse Adoptium\jdk-\;
  4. Try to set JCOBRIDGE_JVMPath at system level e.g. JCOBRIDGE_JVMPath=C:\Program Files\Eclipse Adoptium\jdk-\.


  • One of JCOBRIDGE_JVMPath or JAVA_HOME environment variables or Windows registry (on Windows OSes) shall be available
  • JCOBRIDGE_JVMPath environment variable takes precedence over JAVA_HOME and Windows registry: you can set JCOBRIDGE_JVMPath to C:\Program Files\Eclipse Adoptium\jdk-\bin\server\jvm.dll and avoid to override JVMPath in your code
  • After first initialization steps, JVMPath takes precedence over JCOBRIDGE_JVMPath/JAVA_HOME environment variables or Windows registry