python - sqlalchemy postgresql "Is Null"索引

Question

如何在 PostgreSQL 上使用 sqlalchemy 创建 IS NULL 索引？

PostgreSQL supports this :

an IS NULL or IS NOT NULL condition on an index column can be used with a B-tree index.

我尝试过以下方法:

from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
class Foo(db.Model):
    id = Column(Integer, primary_key=True)
    processing_start_time = Column(DateTime, nullable=True)

    __table_args__ = (
        Index('processing_null_index', 'processing_start_time', is_null=True),
    )

我收到此错误:

/foo/venv/lib/python3.5/site-packages/sqlalchemy/sql/base.py:291: SAWarning: Can't validate argument 'is_null'; can't locate any SQLAlchemy dialect named 'is'
  (k, dialect_name))

Answer 1

IS NULL 不是单独的索引类型。在这种特定情况下，IS NULL 是 partial index 上的条件表达式。 。您可以通过 postresql_where 在 SQLAlchemy 中声明 PostgreSQL 的部分索引夸格:

Index('processing_null_index', processing_start_time, postgresql_where=processing_start_time.is_(None))