utils: generalize utility to find find_constraint_name (#557)

See https://github.com/airbnb/caravel/pull/531

caravel/migrations/versions/1226819ee0e3_fix_wrong_constraint_on_table_columns.py

@@ -12,27 +12,16 @@ down_revision = '956a063c52b3'
 
 from alembic import op
 import sqlalchemy as sa
+from caravel.utils import generic_find_constraint_name
 
 naming_convention = {
     "fk":
     "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
 }
 
-def find_constraint_name(upgrade = True):
+def find_constraint_name(upgrade=True):
-    __table = 'columns'
+    cols = {'column_name'} if upgrade else {'datasource_name'}
-    __cols = {'column_name'} if upgrade else {'datasource_name'}
+    return generic_find_constraint_name(table='columns', columns=cols, referenced='datasources')
-    __referenced = 'datasources'
-    __ref_cols = {'datasource_name'} if upgrade else {'column_name'}
-
-    engine = op.get_bind().engine
-    m = sa.MetaData({})
-    t=sa.Table(__table,m, autoload=True, autoload_with=engine)
-
-    for fk in t.foreign_key_constraints:
-        if fk.referred_table.name == __referenced and \
-            set(fk.column_keys) == __cols:
-            return fk.name
-    return None
 
 def upgrade():
     constraint = find_constraint_name() or 'fk_columns_column_name_datasources'
@@ -47,4 +36,3 @@ def downgrade():
         naming_convention=naming_convention) as batch_op:
         batch_op.drop_constraint(constraint, type_="foreignkey")
         batch_op.create_foreign_key('fk_columns_column_name_datasources', 'datasources', ['column_name'], ['datasource_name'])
-    

caravel/utils.py

@@ -11,7 +11,9 @@ import numpy
 from datetime import datetime
 
 import parsedatetime
+import sqlalchemy as sa
 from dateutil.parser import parse
+from alembic import op
 from flask import flash, Markup
 from flask_appbuilder.security.sqla import models as ab_models
 from markdown import markdown as md
@@ -255,3 +257,18 @@ def readfile(filepath):
     with open(filepath) as f:
         content = f.read()
     return content
+
+
+def generic_find_constraint_name(table, columns, referenced):
+    """
+    Utility to find a constraint name in alembic migrations
+    """
+    engine = op.get_bind().engine
+    m = sa.MetaData({})
+    t = sa.Table(table, m, autoload=True, autoload_with=engine)
+
+    for fk in t.foreign_key_constraints:
+        if fk.referred_table.name == referenced and \
+            set(fk.column_keys) == columns:
+            return fk.name
+    return None