如何从SQLAlchemy结果中获取列名(声明性语法)

Question

我正在金字塔项目中工作,我在SQLAlchemy中使用声明性语法表

"""models.py"""
class Projects(Base):
    __tablename__ = 'projects'
    __table_args__ = {'autoload': True}

我通过使用获得结果

""""views.py"""
session = DBSession()
row_data = session.query(Projects).filter_by(id=1).one()

如何从此结果中获取列名称.

PS:我无法使用此方法,因为我使用的是声明性语法.

Answer 1

您可以执行类似于Foo Stack的答案,而无需通过以下方式执行私有字段:

conn.execute(query).keys()

Answer 2

区别在于ORM和非ORM,而不是声明,这只是ORM的帮助.

Query有一个column_descriptions()为此目的添加的方法::

http://www.sqlalchemy.org/docs/orm/query.html#sqlalchemy.orm.query.Query.column_descriptions

这个例子似乎有一个拼写错误,q.columns但是应该是q.column_descriptions(编辑:修复它).

Answer 3

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import (Column, Index, Date, DateTime, Numeric, BigInteger, String, ForeignKey, Boolean)

Base = declarative_base()

class Project(Base):
    """sqlalchemy ORM for my table."""
    __tablename__ = "table1"
    id = Column("id", BigIntegerID, primary_key=True, autoincrement=True)
    date = Column("date", Date, nullable=False)
    value = Column("value", Numeric(20, 8))
    ...
    ...

然后这将返回列名['id','date','value',...]:

Project.__table__.columns.keys()

或这个

Project.metadata.tables['table1'].columns.keys()

Answer 4

简短的回答是我最终得到了以下解决方案：

column_names = query.statement.columns.keys()

为什么？

我有一个类似的用例，我需要知道查询返回的显式列（即查询不一定包含表类的所有列）。由于该表的大小也很大（数百万个条目），prolibertas 的答案在性能方面并不令人满意。下面是我的 94 列表的性能比较：

# First create a query with 100.000 entries
query = (
            session.query(myTable)
            .limit(100000)
        )

# Then get the column names .. 

column_names = session.execute(query).keys()
# ---> ~ 5.730 seconds

column_names = query.statement.columns.keys()
# ---> ~ 0.003 seconds

Answer 5

只是玩,这个语法将为您提供所有列(所以要解决您的问题,设置查询只查看一个表/对象):

conn.execute(query)._metadata.keys

Answer 6

此链接显示了如何获取您可能需要的有关表、列等的所有元数据。

SQLAlchemy 元数据

上面的许多答案都基于此页面上的信息。假设我们已经声明了一个表。

employees = Table('employees', metadata,
    Column('employee_id', Integer, primary_key=True),
    Column('employee_name', String(60), nullable=False),
    Column('employee_dept', Integer, ForeignKey("departments.department_id"))
)

以下是获取有关表的元数据的一些示例。

# access the column "EMPLOYEE_ID":
employees.columns.employee_id

# or just
employees.c.employee_id

# via string
employees.c['employee_id']

# iterate through all columns
for c in employees.c:
    print(c)

# get the table's primary key columns
for primary_key in employees.primary_key:
    print(primary_key)

# get the table's foreign key objects:
for fkey in employees.foreign_keys:
    print(fkey)

# access the table's MetaData:
employees.metadata

# access the table's bound Engine or Connection, if its MetaData is bound:
employees.bind

# access a column's name, type, nullable, primary key, foreign key
employees.c.employee_id.name
employees.c.employee_id.type
employees.c.employee_id.nullable
employees.c.employee_id.primary_key
employees.c.employee_dept.foreign_keys

# get the "key" of a column, which defaults to its name, but can
# be any user-defined string:
employees.c.employee_name.key

# access a column's table:
employees.c.employee_id.table is employees

# get the table related by a foreign key
list(employees.c.employee_dept.foreign_keys)[0].column.table