diff --git a/lib/Doctrine/ORM/Id/TableGenerator.php b/lib/Doctrine/ORM/Id/TableGenerator.php
index fecc58386..a472a6de3 100644
--- a/lib/Doctrine/ORM/Id/TableGenerator.php
+++ b/lib/Doctrine/ORM/Id/TableGenerator.php
@@ -12,8 +12,48 @@ use Doctrine\ORM\EntityManager;
  */
 class TableGenerator extends AbstractIdGenerator
 {
+    private $_tableName;
+    private $_sequenceName;
+    private $_allocationSize;
+    private $_nextValue;
+    private $_maxValue;
+
+    public function __construct($tableName, $sequenceName = 'default', $allocationSize = 10)
+    {
+        $this->_tableName = $tableName;
+        $this->_sequenceName = $sequenceName;
+        $this->_allocationSize = $allocationSize;
+    }
+
     public function generate(EntityManager $em, $entity)
     {
-        throw new \BadMethodCallException(__CLASS__."::".__FUNCTION__." not implemented.");
+        if ($this->_maxValue === null || $this->_nextValue == $this->_maxValue) {
+            // Allocate new values
+            $conn = $em->getConnection();
+            if ($conn->getTransactionNestingLevel() == 0) {
+
+                // use select for update
+                $sql = $conn->getDatabasePlatform()->getTableHiLoCurrentValSql($this->_tableName, $this->_sequenceName);
+                $currentLevel = $conn->fetchColumn($sql);
+                if ($currentLevel != null) {
+                    $this->_nextValue = $currentLevel;
+                    $this->_maxValue = $this->_nextValue + $this->_allocationSize;
+
+                    $updateSql = $conn->getDatabasePlatform()->getTableHiLoUpdateNextValSql(
+                        $this->_tableName, $this->_sequenceName, $this->_allocationSize
+                    );
+                    
+                    if ($conn->executeUpdate($updateSql, array(1 => $currentLevel, 2 => $currentLevel+1)) !== 1) {
+                        // no affected rows, concurrency issue, throw exception
+                    }
+                } else {
+                    // no current level returned, TableGenerator seems to be broken, throw exception
+                }
+            } else {
+                // only table locks help here, implement this or throw exception?
+                // or do we want to work with table locks exclusively?
+            }
+        }
+        return $this->_nextValue++;
     }
 }
\ No newline at end of file
diff --git a/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php b/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
index 7f47b6d27..89dc54935 100644
--- a/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
+++ b/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
@@ -609,6 +609,10 @@ class ClassMetadataInfo
         }
 
         $this->columnNames[$mapping['fieldName']] = $mapping['columnName'];
+        if (isset($this->fieldNames[$mapping['columnName']]) || ($this->discriminatorColumn != null && $this->discriminatorColumn['name'] == $mapping['columnName'])) {
+            throw MappingException::duplicateColumnName($this->name, $mapping['columnName']);
+        }
+
         $this->fieldNames[$mapping['columnName']] = $mapping['fieldName'];
 
         // Complete id mapping
@@ -1033,7 +1037,7 @@ class ClassMetadataInfo
     public function mapField(array $mapping)
     {
         $this->_validateAndCompleteFieldMapping($mapping);
-        if (isset($this->fieldMappings[$mapping['fieldName']])) {
+        if (isset($this->fieldMappings[$mapping['fieldName']]) || isset($this->associationMappings[$mapping['fieldName']])) {
             throw MappingException::duplicateFieldMapping($this->name, $mapping['fieldName']);
         }
         $this->fieldMappings[$mapping['fieldName']] = $mapping;
@@ -1145,7 +1149,7 @@ class ClassMetadataInfo
     protected function _storeAssociationMapping(AssociationMapping $assocMapping)
     {
         $sourceFieldName = $assocMapping->sourceFieldName;
-        if (isset($this->associationMappings[$sourceFieldName])) {
+        if (isset($this->fieldMappings[$sourceFieldName]) || isset($this->associationMappings[$sourceFieldName])) {
             throw MappingException::duplicateFieldMapping($this->name, $sourceFieldName);
         }
         $this->associationMappings[$sourceFieldName] = $assocMapping;
@@ -1232,6 +1236,10 @@ class ClassMetadataInfo
     public function setDiscriminatorColumn($columnDef)
     {
         if ($columnDef !== null) {
+            if (isset($this->fieldNames[$columnDef['name']])) {
+                throw MappingException::duplicateColumnName($this->name, $columnDef['name']);
+            }
+
             if ( ! isset($columnDef['name'])) {
                 throw MappingException::nameIsMandatoryForDiscriminatorColumns($this->name, $columnDef);
             }
diff --git a/lib/Doctrine/ORM/Mapping/MappingException.php b/lib/Doctrine/ORM/Mapping/MappingException.php
index 175021b4a..ae0907728 100644
--- a/lib/Doctrine/ORM/Mapping/MappingException.php
+++ b/lib/Doctrine/ORM/Mapping/MappingException.php
@@ -185,4 +185,14 @@ class MappingException extends \Doctrine\ORM\ORMException
             "does not exist."
         );
     }
+
+    /**
+     * @param  string $className
+     * @param  string $columnName
+     * @return self
+     */
+    public static function duplicateColumnName($className, $columnName)
+    {
+        return new self("Duplicate definition of column '".$columnName."' on entity '".$className."' in a field or discriminator column mapping.");
+    }
 }
\ No newline at end of file