#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();
 	}