Remove State.LastSchema method (#909)

Remove the `State.LastSchema` method and replace its usages with
`state.ReadSchema` instead.

For validating migrations, we always want to validate against the
current state of the db schema.

Author: andrew-farries

pkg/roll/execute.go

@@ -19,7 +19,7 @@ func (m *Roll) Validate(ctx context.Context, migration *migrations.Migration) er
 	if m.skipValidation {
 		return nil
 	}
-	lastSchema, err := m.state.LastSchema(ctx, m.schema)
+	lastSchema, err := m.state.ReadSchema(ctx, m.schema)
 	if err != nil {
 		return err
 	}

pkg/state/state.go

@@ -328,27 +328,6 @@ func (s *State) Start(ctx context.Context, schemaname string, migration *migrati
 	return err
 }
 
-func (s *State) LastSchema(ctx context.Context, schemaname string) (*schema.Schema, error) {
-	stmt := fmt.Sprintf(`SELECT COALESCE(
-		(SELECT resulting_schema FROM %[1]s.migrations WHERE schema=$1 AND name=%[1]s.latest_version($1)),
-		%[1]s.read_schema($1))`,
-		pq.QuoteIdentifier(s.schema))
-
-	var rawSchema string
-	err := s.pgConn.QueryRowContext(ctx, stmt, schemaname).Scan(&rawSchema)
-	if err != nil {
-		return nil, err
-	}
-
-	var unmarshalledSchema schema.Schema
-	err = json.Unmarshal([]byte(rawSchema), &unmarshalledSchema)
-	if err != nil {
-		return nil, fmt.Errorf("unable to unmarshal schema: %w", err)
-	}
-
-	return &unmarshalledSchema, nil
-}
-
 // Complete marks a migration as completed
 func (s *State) Complete(ctx context.Context, schema, name string) error {
 	res, err := s.pgConn.ExecContext(ctx, fmt.Sprintf("UPDATE %[1]s.migrations SET done=$1, resulting_schema=(SELECT %[1]s.read_schema($2)) WHERE schema=$2 AND name=$3 AND done=$4", pq.QuoteIdentifier(s.schema)), true, schema, name, false)

pkg/state/state_test.go

@@ -38,7 +38,7 @@ func TestSchemaOptionIsRespected(t *testing.T) {
 		}
 
 		// check that we can retrieve the already existing table
-		currentSchema, err := state.LastSchema(ctx, "public")
+		currentSchema, err := state.ReadSchema(ctx, "public")
 		assert.NoError(t, err)
 
 		assert.Equal(t, 1, len(currentSchema.Tables))