#435 - Duplicate foreign key name with ManyToMany relations

src/main/java/com/avaje/ebean/dbmigration/model/MCompoundForeignKey.java

@@ -14,7 +14,7 @@ import java.util.List;
  */
 public class MCompoundForeignKey {
 
-  private final String name;
+  private String name;
   private final String referenceTable;
   private final List<String> columns = new ArrayList<String>();
   private final List<String> referenceColumns = new ArrayList<String>();
@@ -47,6 +47,28 @@ public class MCompoundForeignKey {
     return fk;
   }
 
+  /**
+   * Add a counter to the foreign key and index names to avoid duplication.
+   */
+  public void addNameSuffix(int counter) {
+    this.name = name + "_" + counter;
+    this.indexName = indexName + "_" + counter;
+  }
+
+  /**
+   * Return the foreign key name.
+   */
+  public String getName() {
+    return name;
+  }
+
+  /**
+   * Return the index name.
+   */
+  public String getIndexName() {
+    return indexName;
+  }
+
   /**
    * Return the columns making up the foreign key in order.
    */

src/main/java/com/avaje/ebean/dbmigration/model/MTable.java

@@ -14,6 +14,7 @@ import com.avaje.ebean.dbmigration.migration.UniqueConstraint;
 import java.math.BigInteger;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -482,4 +483,32 @@ public class MTable {
     return (value == 0) ? null : BigInteger.valueOf(value);
   }
 
+  /**
+   * Check if there are duplicate foreign keys.
+   * <p>
+   *   This can occur when an ManyToMany relates back to itself.
+   * </p>
+   */
+  public void checkDuplicateForeignKeys() {
+
+    if (hasDuplicateForeignKeys()) {
+      int counter = 1;
+      for (MCompoundForeignKey fk : compoundKeys) {
+        fk.addNameSuffix(counter++);
+      }
+    }
+  }
+
+  /**
+   * Return true if the foreign key names are not unique.
+   */
+  private boolean hasDuplicateForeignKeys() {
+    Set<String> fkNames = new HashSet<String>();
+    for (MCompoundForeignKey fk : compoundKeys) {
+      if (!fkNames.add(fk.getName())) {
+        return true;
+      }
+    }
+    return false;
+  }
 }

src/main/java/com/avaje/ebean/dbmigration/model/build/ModelBuildIntersectionTable.java

@@ -47,6 +47,8 @@ public class ModelBuildIntersectionTable {
 
 		BeanDescriptor<?> targetDesc = manyProp.getTargetDescriptor();
 		buildFkConstraints(targetDesc, tableJoin.columns(), false);
+
+    intersectionTable.checkDuplicateForeignKeys();
 	}
 
 	

src/test/java/com/avaje/tests/m2m/TestM2MSelfRelationship.java

@@ -0,0 +1,29 @@
+package com.avaje.tests.m2m;
+
+import com.avaje.ebean.BaseTestCase;
+import com.avaje.ebean.Ebean;
+import com.avaje.tests.model.m2m.MnyTopic;
+import org.junit.Test;
+
+/**
+ * Added to test DDL generation for ManyToMany related back to itself.
+ */
+public class TestM2MSelfRelationship extends BaseTestCase {
+
+  @Test
+  public void test() {
+
+    Ebean.getDefaultServer();
+
+    // Create 2 roles r0 and r1
+    MnyTopic r0 = new MnyTopic("r0");
+    MnyTopic r1 = new MnyTopic("r1");
+
+    // Save r1 and r2
+    Ebean.save(r0);
+    Ebean.save(r1);
+
+    r0.getSubTopics().add(r1);
+    Ebean.save(r0);
+  }
+}

src/test/java/com/avaje/tests/model/m2m/MnyTopic.java

@@ -0,0 +1,67 @@
+package com.avaje.tests.model.m2m;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+import javax.persistence.JoinColumn;
+import javax.persistence.JoinTable;
+import javax.persistence.ManyToMany;
+import javax.persistence.Version;
+import java.util.List;
+
+@Entity
+public class MnyTopic {
+
+  @Id
+  Long id;
+
+  String name;
+
+  @Version
+  Long version;
+
+  @ManyToMany
+  @JoinTable(name = "subtopics",
+      joinColumns = @JoinColumn(name = "topic", referencedColumnName = "id"),
+      inverseJoinColumns = @JoinColumn(name = "subtopic", referencedColumnName = "id"))
+  List<MnyTopic> subTopics;
+
+  public MnyTopic() {
+
+  }
+
+  public MnyTopic(String name) {
+    this.name = name;
+  }
+
+  public Long getId() {
+    return id;
+  }
+
+  public void setId(Long id) {
+    this.id = id;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public void setName(String name) {
+    this.name = name;
+  }
+
+  public Long getVersion() {
+    return version;
+  }
+
+  public void setVersion(Long version) {
+    this.version = version;
+  }
+
+  public List<MnyTopic> getSubTopics() {
+    return subTopics;
+  }
+
+  public void setSubTopics(List<MnyTopic> subTopics) {
+    this.subTopics = subTopics;
+  }
+}