diff --git a/core/src/main/groovy/com/jdbernard/wdiwtlt/db/DbApi.groovy b/core/src/main/groovy/com/jdbernard/wdiwtlt/db/DbApi.groovy
index 952df67..c084367 100644
--- a/core/src/main/groovy/com/jdbernard/wdiwtlt/db/DbApi.groovy
+++ b/core/src/main/groovy/com/jdbernard/wdiwtlt/db/DbApi.groovy
@@ -34,7 +34,7 @@ public class DbApi {
     public void shutdown() { dataSource.shutdown() }
 
     /// ### Common
-    public def getAll(Class modelClass, String orderClause = null) {
+    public <M extends Model> List<M> getAll(Class<M> modelClass, String orderClause = null) {
         def query = new StringBuilder()
         query.append('SELECT * FROM ')
              .append(pluralize(nameFromModel(modelClass.simpleName)))
@@ -46,19 +46,19 @@ public class DbApi {
         logger.debug('Selecting models.\n\tSQL: {}', query)
         return sql.rows(query).collect { recordToModel(modelClass, it) } }
 
-    public List<UUID> getAllIds(Class modelClass) {
+    public List<UUID> getAllIds(Class<? extends Model> modelClass) {
         String query = 'SELECT id FROM ' +
           pluralize(nameFromModel(modelClass.simpleName))
 
       logger.debug('Selecting model ids.\n\tSQL: {}', query)
       return sql.rows(query).collect { it.id } }
 
-    public Model getById(Class<? extends Model> modelClass, UUID id) {
+    public <M extends Model> M getById(Class<M> modelClass, UUID id) {
         def model = modelClass.newInstance()
         model.id = id
         return refresh(model) }
 
-    public List<Model> getByIdLike(Class<? extends Model> modelClass,
+    public <M extends Model> List<M> getByIdLike(Class<M> modelClass,
     String partialId) {
         String likeVal = partialId + '%'
         String query = new StringBuilder()
@@ -72,7 +72,7 @@ public class DbApi {
         return sql.rows(query, likeVal)
           .collect { recordToModel(modelClass, it) } }
 
-    public def refresh(def model) {
+    public <M extends Model> M refresh(M model) {
         def query = new StringBuilder()
             .append('SELECT * FROM ')
             .append(pluralize(nameFromModel(model.class.simpleName)))
@@ -84,7 +84,7 @@ public class DbApi {
         if (!result) return null
         return updateModel(result, model) }
 
-    public def getByName(Class modelClass, String name) {
+    public <M extends Model> List<M> getByName(Class<M> modelClass, String name) {
         def query = new StringBuilder()
             .append('SELECT * FROM ')
             .append(pluralize(nameFromModel(modelClass.simpleName)))
@@ -94,8 +94,8 @@ public class DbApi {
         logger.debug('Selecting model.\n\tSQL: {}\n\tPARAMS: {}', query, name)
         return sql.rows(query, [name]).collect { recordToModel(modelClass, it) } }
 
-    public def getBy(Class modelClass, List<String> columns,
-    List<Object> values) {
+    public <M extends Model> List<M> getBy(Class<M> modelClass,
+    List<String> columns, List values) {
         def query = new StringBuilder()
             .append('SELECT * FROM ')
             .append(pluralize(nameFromModel(modelClass.simpleName)))
@@ -107,8 +107,8 @@ public class DbApi {
         return sql.rows(query, values)
             .collect { recordToModel(modelClass, it) } }
 
-    public def getLike(Class modelClass, List<String> columns,
-    List<Object> values) {
+    public <M extends Model> List<M> getLike(Class<M> modelClass,
+    List<String> columns, List values) {
         values = values.collect { "%$it%".toString() }
         String query = new StringBuilder()
             .append('SELECT * FROM ')
@@ -121,7 +121,7 @@ public class DbApi {
         return sql.rows(query, values)
             .collect { recordToModel(modelClass, it) } }
 
-    public def getWhere(Class modelClass, Map criteria) {
+    public <M extends Model> List<M> getWhere(Class<M> modelClass, Map criteria) {
         switch(modelClass) {
             case Album:      return getAlbumsWhere(criteria)
             case Artist:     return getArtistsWhere(criteria)
@@ -130,11 +130,11 @@ public class DbApi {
             case Playlist:   return getPlaylistsWhere(criteria)
             case Tag:        return getTagsWhere(criteria) } }
 
-    public def save(def model) {
+    public Model save(Model model) {
         if (model.id) return update(model)
         else return create(model) }
 
-    public def update(def model) {
+    public Model update(Model model) {
         def setClauses = []
         def params = []
 
@@ -144,7 +144,7 @@ public class DbApi {
                 setClauses << '"' + nameFromModel(field.name) + '"= ?'
                 params << field.get(model) }
 
-        def query = new StringBuilder()
+        String query = new StringBuilder()
             .append('UPDATE ')
             .append(pluralize(nameFromModel(model.class.simpleName)))
             .append(' SET ')
@@ -159,7 +159,7 @@ public class DbApi {
             sql.executeUpdate(query, params)
             return refresh(model) } }
 
-    public def create(def model) {
+    public Model create(Model model) {
         def columns = []
         def params = []
 
@@ -183,7 +183,7 @@ public class DbApi {
         sql.executeInsert(query, params)
         return model }
 
-    public def delete(def model) {
+    public int delete(Model model) {
         def query = new StringBuilder()
             .append('DELETE FROM ')
             .append(pluralize(nameFromModel(model.class.simpleName)))
@@ -195,8 +195,8 @@ public class DbApi {
         sql.execute(query, [model.id])
         return sql.updateCount }
 
-    public def associate(Class modelClass1, Class modelClass2 ,
-    UUID firstId, UUID secondId) {
+    public def associate(Class<? extends Model> modelClass1,
+    Class<? extends Model> modelClass2 , UUID firstId, UUID secondId) {
         String linkTable = pluralize(nameFromModel(modelClass1.simpleName)) +
                      '_' + pluralize(nameFromModel(modelClass2.simpleName))
         String col1 = nameFromModel(modelClass1.simpleName) + '_id'
@@ -218,7 +218,7 @@ public class DbApi {
                     query, params)
                 return sql.execute(query, params) } } }
 
-    public def associate(def m1, def m2) {
+    public def associate(Model m1, Model m2) {
         return associate(m1.class, m2.class, m1.id, m2.id) }
 
     /// ### Album-specific methods
@@ -905,7 +905,7 @@ public class DbApi {
             field.set(model, record[nameFromModel(field.name)]) }
         return model }
 
-    static def recordToModel(Class modelClass, def record) {
+    static <M extends Model> M recordToModel(Class<M> modelClass, def record) {
         if (record == null) return null
 
         def model = modelClass.newInstance()
@@ -915,7 +915,7 @@ public class DbApi {
 
         return model }
 
-    static def modelToRecord(def model) {
+    static def modelToRecord(Model model) {
         if (model == null) return null
 
         def record = [:]