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Datahike Java Examples

This directory contains example applications demonstrating the Datahike Java API.

Prerequisites

  • Java 17 or higher (required for text blocks and modern Java features)
  • Maven 3.6+

Running the Examples

Option 1: Maven Exec (Recommended)

Run examples directly with Maven:

# Quick Start
mvn compile exec:java -Dexec.mainClass="examples.QuickStart"

# Schema Example
mvn compile exec:java -Dexec.mainClass="examples.SchemaExample"

# Time Travel Example
mvn compile exec:java -Dexec.mainClass="examples.TimeTravelExample"

Option 2: Build and Run JAR

Build the project and run the JAR:

# Build
mvn clean package

# Run (using QuickStart as main class from pom.xml)
java -jar target/datahike-java-examples-1.0.0-SNAPSHOT.jar

# Or run specific examples
java -cp target/datahike-java-examples-1.0.0-SNAPSHOT.jar examples.SchemaExample

Option 3: IDE

Import the Maven project into your IDE (IntelliJ IDEA, Eclipse, VSCode) and run the main classes directly.

Examples

QuickStart.java

Basic introduction to Datahike:

  • Database configuration with builder pattern
  • Creating and connecting to databases
  • Transacting data with Java Maps
  • Querying with Datalog
  • Updates and cleanup

Key concepts: Builder pattern, basic queries, CRUD operations

SchemaExample.java

Schema definition and validation:

  • Defining attributes with type constraints
  • Unique constraints (identity vs value)
  • Reference types for relationships
  • Cardinality (one vs many)
  • Using Keywords constants

Key concepts: Schema definition, relationships, data validation

TimeTravelExample.java

Historical queries and time travel:

  • Querying database state at specific points in time
  • Using asOf for point-in-time queries
  • Using since for change tracking
  • Querying full history
  • Transaction metadata

Key concepts: Immutability, history, audit trails

Project Structure

examples/java/
├── pom.xml                                 # Maven configuration
├── README.md                               # This file
└── src/main/java/examples/
    ├── QuickStart.java                     # Basic usage
    ├── SchemaExample.java                  # Schema definition
    └── TimeTravelExample.java              # Time travel queries

Using Datahike in Your Project

To use Datahike in your own Maven project, add to your pom.xml:

<repositories>
    <repository>
        <id>clojars</id>
        <url>https://repo.clojars.org/</url>
    </repository>
</repositories>

<dependencies>
    <dependency>
        <groupId>io.replikativ</groupId>
        <artifactId>datahike</artifactId>
        <version>LATEST_VERSION</version>
    </dependency>
</dependencies>

For Gradle:

repositories {
    maven { url "https://repo.clojars.org/" }
}

dependencies {
    implementation 'io.replikativ:datahike:LATEST_VERSION'
}

Note: Replace LATEST_VERSION with the latest published version from Clojars.

Key Java API Classes

  • Datahike - Main API with all database operations
  • Database - Fluent builder for configuration
  • Keywords - Pre-defined constants for schema
  • SchemaFlexibility - Enum for schema modes
  • Util - Low-level utilities (map, vec, kwd)
  • EDN - EDN data type constructors

Further Reading

Troubleshooting

Build fails with "Could not find artifact"

  • Ensure Clojars repository is configured
  • Check internet connection
  • Try mvn clean install -U to force update

Runtime errors about Clojure

  • Datahike includes Clojure as a dependency
  • Check for dependency conflicts with mvn dependency:tree

ClassCastException in query results

  • Query results are Clojure collections (Set, List, Map)
  • Cast appropriately: (Set<?>) Datahike.q(...)

License

Eclipse Public License 1.0 (EPL-1.0)