App Engine does not create local_db.bin

Question

Im new with appengine, Im using appengine version 1.8.7(also happens to me in 1.8.6), and trying to add maven to the project.

When I persist an entity the log is the following:

[INFO] nov 07, 2013 5:38:33 PM com.google.appengine.api.datastore.dev.LocalDatastoreService init
[INFO] INFO: Local Datastore initialized:
[INFO]  Type: High Replication
[INFO]  Storage: D:\Projects\JEE\myapp\tmp\local_db.bin
[INFO] nov 07, 2013 5:38:33 PM com.google.appengine.api.datastore.dev.LocalDatastoreService load
[INFO] INFO: The backing store, D:\Projects\JEE\myapp\tmp\local_db.bin, does not exist. It will be created.

My issue is that the local_db.bin is not created. And for example if I try to make a search of my peristed entity an errors appears.

[INFO] java.lang.IllegalArgumentException: Type com.harriague.myapp.dao.entities.Travel is not a known entity type
[INFO]  at org.datanucleus.api.jpa.metamodel.MetamodelImpl.entity(MetamodelImpl.java:193)

...

This is my entity class:

package com.harriague.myapp.dao.entities;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Column;

import com.google.appengine.api.datastore.Key;

@Entity(name = "Travel")
public class Travel {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Key travelId;

    @Column(name = "name")
    private String name;

    public Travel() {

    }

    public Key getTravelId() {
        return travelId;
    }

    public void setTravelId(Key travelId) {
        this.travelId = travelId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Here is mi pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>

    <groupId>com.harriague</groupId>
    <artifactId>myapp</artifactId>


    <properties>
        <appengine.app.version>1</appengine.app.version>
        <appengine.target.version>1.8.7</appengine.target.version>
        <datanucleus-core.version>3.1.3</datanucleus-core.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <!-- Compile/runtime dependencies -->
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-api-1.0-sdk</artifactId>
            <version>${appengine.target.version}</version>
        </dependency>
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-endpoints</artifactId>
            <version>${appengine.target.version}</version>
        </dependency>
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-api-labs</artifactId>
            <version>${appengine.target.version}</version>
        </dependency>
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm</artifactId>
            <version>4.0</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>

        <!-- JSON -->
        <dependency>
            <groupId>com.googlecode.json-simple</groupId>
            <artifactId>json-simple</artifactId>
            <version>1.1.1</version>
        </dependency>

        <!-- Test Dependencies -->
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-testing</artifactId>
            <version>${appengine.target.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.google.appengine</groupId>
            <artifactId>appengine-api-stubs</artifactId>
            <version>${appengine.target.version}</version>
            <scope>test</scope>
        </dependency>

        <!-- Spring framework -->
        <!-- 
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring</artifactId>
            <version>2.5.6</version>
        </dependency>
        -->

        <!-- Javax persistence -->
        <dependency>
            <groupId>org.datanucleus</groupId>
            <artifactId>datanucleus-core</artifactId>
            <version>${datanucleus-core.version}</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.geronimo.specs</groupId>
            <artifactId>geronimo-jpa_2.0_spec</artifactId>
            <version>1.1</version>
        </dependency>
        <dependency>
            <groupId>org.datanucleus</groupId>
            <artifactId>datanucleus-api-jpa</artifactId>
            <version>3.1.3</version>
        </dependency>
        <dependency>
            <groupId>com.google.appengine.orm</groupId>
            <artifactId>datanucleus-appengine</artifactId>
            <version>2.1.2</version>
            <!-- Need to exclude the enhancer since it interfere with the enhancer plugin. -->
            <exclusions>
              <exclusion>
                <groupId>org.datanucleus</groupId>
                <artifactId>datanucleus-enhancer</artifactId>
              </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <version>2.5.1</version>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.6</source>
                    <target>1.6</target>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.3</version>
                <configuration>
                    <archiveClasses>true</archiveClasses>
                    <webResources>
                        <!-- in order to interpolate version from pom into appengine-web.xml -->
                        <resource>
                            <directory>${basedir}/src/main/webapp/WEB-INF</directory>
                            <filtering>true</filtering>
                            <targetPath>WEB-INF</targetPath>
                        </resource>
                        <!--
                        <resource>
                            <directory>${basedir}/src/main/resources</directory>
                        </resource>
                        -->
                    </webResources>
                </configuration>
            </plugin>

            <plugin>
                <groupId>com.google.appengine</groupId>
                <artifactId>appengine-maven-plugin</artifactId>
                <version>${appengine.target.version}</version>
                <configuration>
                    <enableJarClasses>false</enableJarClasses>
                    <!--<jvmFlags>
                        <jvmFlag>-Ddatastore.backing_store=${basedir}\local_db.bin</jvmFlag>
                    </jvmFlags>
                    -->
                    <jvmFlags>
                        <jvmFlag>-Dappengine.generated.dir=${basedir}/tmp</jvmFlag>
                    </jvmFlags>
                    <!--
                    <jvmFlags>
                        <jvmFlag>-Xdebug</jvmFlag>
                        <jvmFlag>-Xrunjdwp:transport=dt_socket,address=8080,server=y,suspend=y</jvmFlag>
                    </jvmFlags>
                    -->
                    <disableUpdateCheck>true</disableUpdateCheck>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.datanucleus</groupId>
                <artifactId>maven-datanucleus-plugin</artifactId>
                <version>3.1.1</version>
                <configuration>
                    <api>JPA</api>
                    <fork>false</fork>
                    <persistenceUnitName>transactions-optional</persistenceUnitName>
                    <verbose>true</verbose>
                </configuration>
                <executions>
                    <execution>
                        <phase>process-classes</phase>
                        <goals>
                            <goal>enhance</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

In addition, if this project is created with the appengine eclipse plugin, nothing of this happends and me code works fine.

Thanks in advance

Answer 1

In Android Studio or Gradle build system, you can use jvmFlags to overwrite default path. Add below code to build.gradle

appengine {
    jvmFlags=['-Ddatastore.backing_store=../../../local_db.bin']
}

Answer 2

I have been using App Engine for a while, but recently converted a project to use Maven and the Maven plugin. I had a very similar issue - it appears creating a local_db.bin file is not part of the start-up actions.

However, when I tried to read from the datastore, a log message indicated that since no local_db.bin was found, that one would be created (sorry, I don't have the exact log message handy). I was able to use the application normally after that, the local_db was indeed created.

However, I noticed that it was creating the local_db.bin file in the target directory, not in the src directory, so each time I re-started my server the local_db.bin file gets wiped out and has to be re-created. So, once local_db.bin gets created, you can find it in the target/your_SNAPSHOT/WEB-INF/appengine-generated and copy it into your src/main/webapp/WEB-INF/appengine-generated dirctory. It should then get included in your target directory when you do a build.

Please note that this has some drawbacks - any data changes you make in future sessions aren't persisted as they are stored in the local_db.bin that gets wiped out each build, but you can at least get a base of data to use. Hopefully I (or someone else here) can find a better way to get this to work.