1.定义配置项
首先定义两个数据库的配置信息
# PostgreSQL database configuration DB_USERNAME=postgres DB_PASSWORD=passord DB_HOST=127.0.0.1 DB_PORT=5432 DB_DATABASE=test # mysql database configuration DB_USERNAME_MYSQL=root DB_PASSWORD_MYSQL=password DB_HOST_MYSQL=127.0.0.1 DB_PORT_MYSQL=3306 DB_DATABASE_MYSQL=test
2.定义Config类
首先读取上面的数据库配置项。
“db_credentials ”和“db_mysql_credentials”是我储存对应数据库配置的自定义字段，随意起名即可。
“self.SQLALCHEMY_DATABASE_URI”字段名代表sqlalchemy的主数据库，这里我使用的是postgres，里面按照文档要求填上对应的请求地址。
“self.SQLALCHEMY_BINDS”可以理解为副数据库，可以把其他数据库都写在这里，其值是dict格式。格式为{"key":"databaseUri"}。每个数据库都必须以唯一的键值区分，键值按自己喜好取就行。mysql1，mysql2，mysql3什么的....
"self.SQLALCHEMY_ENGINE_OPTIONS"代表连接池大小
“self.SQLALCHEMY_ECHO”代表sqlalchemy在每次请求时是否在控制台打印sql语句
注意：
SQLAlchemy采用的是加载对应数据库DBAPI 的方式来连接的，而具体加载哪个DBAPI 是你在数据库URI中声明的，如“mysql+pymysql”代表使用PyMySQL连接mysql，也就是说你需要先安装PyMySQL库。这其实和使用java时用JDBC映射的方式连接mysql很像
pip install PyMySQLConfig代码内容:
class Config:
"""Application configuration class."""
def __init__(self):
# ------------------------
# Database Configurations.
# ------------------------
db_credentials = {
key: get_env(key) for key in
['DB_USERNAME', 'DB_PASSWORD', 'DB_HOST', 'DB_PORT', 'DB_DATABASE', 'DB_CHARSET']
}
self.SQLALCHEMY_DATABASE_URI_SCHEME = get_env('SQLALCHEMY_DATABASE_URI_SCHEME')
db_extras = f"?client_encoding={db_credentials['DB_CHARSET']}" if db_credentials['DB_CHARSET'] else ""
self.SQLALCHEMY_DATABASE_URI = f"{self.SQLALCHEMY_DATABASE_URI_SCHEME}://{db_credentials['DB_USERNAME']}:{db_credentials['DB_PASSWORD']}@{db_credentials['DB_HOST']}:{db_credentials['DB_PORT']}/{db_credentials['DB_DATABASE']}{db_extras}"
db_mysql_credentials = {
key: get_env(key) for key in
['DB_USERNAME_MYSQL', 'DB_PASSWORD_MYSQL', 'DB_HOST_MYSQL', 'DB_PORT_MYSQL', 'DB_DATABASE_MYSQL']
}
# password = db_mysql_credentials['DB_PASSWORD_MYSQL']
# pwd = parse.quote_plus(password)
self.SQLALCHEMY_BINDS = {
"mysqlkey": f"mysql+pymysql://{db_mysql_credentials['DB_USERNAME_MYSQL']}:{db_mysql_credentials['DB_PASSWORD_MYSQL']}@{db_mysql_credentials['DB_HOST_MYSQL']}:{db_mysql_credentials['DB_PORT_MYSQL']}/{db_mysql_credentials['DB_DATABASE_MYSQL']}?charset=utf8mb4"
}
self.SQLALCHEMY_ENGINE_OPTIONS = {
'pool_size': int(get_env('SQLALCHEMY_POOL_SIZE')),
'max_overflow': int(get_env('SQLALCHEMY_MAX_OVERFLOW')),
'pool_recycle': int(get_env('SQLALCHEMY_POOL_RECYCLE')),
'pool_pre_ping': get_bool_env('SQLALCHEMY_POOL_PRE_PING'),
'connect_args': {'options': '-c timezone=UTC'},
}
self.SQLALCHEMY_ECHO = get_bool_env('SQLALCHEMY_ECHO')3.初始化SQLAlchemy
编写好Config类后，就可以初始化sqlalchemy了。
from flask_sqlalchemy import SQLAlchemy
from myconfig import Config
from flask import Flask
import flask_migrate
app = Flask()
app.config.from_object(Config())
db = SQLAlchemy()
db.init_app(app)
flask_migrate.Migrate(app, db)4.定义不同数据库的表结构
如果表所对应的数据库是通过“self.SQLALCHEMY_DATABASE_URI”字段绑定到SQLAlchemy上的，那么它所对应的类不需要做额外的修改，SQLAlchemy默认使用主数据库。
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
class Setup(db.Model):
__tablename__ = 'setups'
__table_args__ = (
db.PrimaryKeyConstraint('version', name='setup_pkey'),
)
version = db.Column(db.String(255), nullable=False)
setup_at = db.Column(db.DateTime, nullable=False, server_default=db.text('CURRENT_TIMESTAMP(0)'))如果表所对应的数据库是通过“self.SQLALCHEMY_BINDS”字段的方式绑定到SQLAlchemy上的，那么就需要在类的开头用__bind_key__声明这张表是在哪一个数据库上，值填写你在“self.SQLALCHEMY_BINDS”的dict上对应数据库的key，我的是“mysqlkey”，其他照旧。
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
class MysqlTestTable(db.Model):
__bind_key__ = "mysqlkey"
__tablename__ = "test_table"
__table_args__ = (
db.PrimaryKeyConstraint("id", name="PRIMARY"),
db.Index("idx_unique", "phoneNo"),
)
id = db.Column(db.BigInteger, primary_key=True, autoincrement=True)
phoneNo = db.Column(db.BigInteger, nullable=False, comment="")
name = db.Column(db.String(20), nullable=False, comment="")
