英文:
Executing SQL query with variable number of named parameters in Golang
问题
我有一个 PostgreSQL 函数,它接受可变数量的命名参数,并返回相应项的列表:
CREATE OR REPLACE FUNCTION read_user(
_id BIGINT DEFAULT NULL,
_phone VARCHAR(30) DEFAULT NULL,
_type VARCHAR(15) DEFAULT NULL,
_last VARCHAR(50) DEFAULT NULL,
_first VARCHAR(50) DEFAULT NULL
)
RETURNS setof T_USERS
AS $$
BEGIN
RETURN QUERY
SELECT * FROM T_USERS
WHERE ( id = _id OR _id IS NULL )
AND ( phone = _phone OR _phone IS NULL )
AND ( type = _type OR _type IS NULL )
AND ( last = _last OR _last IS NULL )
AND ( first = _first OR _first IS NULL );
EXCEPTION WHEN others THEN
RAISE WARNING 'Transaction failed and was rolled back';
RAISE NOTICE '% %', SQLERRM, SQLSTATE;
END
$$ LANGUAGE plpgsql;
我可以运行类似这样的多态查询:
SELECT read_user(_id := 2);
SELECT read_user(_first := 'John', _last := 'Doe');
在 Golang 中,我可以这样做:
stmt, err := db.Prepare("SELECT read_user(_id = ?)")
但是,如何使用可变数量的 read_user
参数做同样的事情呢?我正在使用 pq
驱动程序 https://github.com/lib/pq。
英文:
So I have this PostgreSQL function, which takes variable number of named arguments and returns list of corresponding items:
CREATE OR REPLACE FUNCTION read_user(
_id BIGINT DEFAULT NULL,
_phone VARCHAR(30) DEFAULT NULL,
_type VARCHAR(15) DEFAULT NULL,
_last VARCHAR(50) DEFAULT NULL,
_first VARCHAR(50) DEFAULT NULL
)
RETURNS setof T_USERS
AS $$
BEGIN
RETURN QUERY
SELECT * FROM T_USERS
WHERE ( id = _id OR _id IS NULL )
AND ( phone = _phone OR _phone IS NULL )
AND ( type = _type OR _type IS NULL )
AND ( last = _last OR _last IS NULL )
AND ( first = _first OR _first IS NULL );
EXCEPTION WHEN others THEN
RAISE WARNING 'Transaction failed and was rolled back';
RAISE NOTICE '% %', SQLERRM, SQLSTATE;
END
$$ LANGUAGE plpgsql;
So I can run polymorphic queries like these:
SELECT read_user(_id := 2);
SELECT read_user(_first := 'John', _last := 'Doe');
In Golang I can make something like:
stmt, err := db.Prepare("SELECT read_user(_id = ?)")
But how can I do the same, but with variable amount of read_user
arguments? I'm using pq
driver https://github.com/lib/pq.
答案1
得分: 4
你可以通过列举所有参数及其占位符来构建自己的语句,然后在没有参数值的地方显式地传递nil
。
stmt, err := db.Prepare("SELECT read_user(_id := $1, _phone := $2, _type := $3, _last := $4, _first := $5)")
if err != nil {
// ...
}
stmt.Query(2, nil, nil, nil, nil) // 结果应等同于 `SELECT read_user(_id := 2)`
stmt.Query(nil, nil, nil, "Doe", "John") // 结果应等同于 `SELECT read_user(_first := 'John', _last := 'Doe')`
如果你也想在Go中使用命名参数,你可以创建一个结构体类型来表示参数,并创建一个包装函数,将该参数类型的字段映射到查询中:
type readUserParams struct {
Id interface{}
Phone interface{}
Type interface{}
Last interface{}
First interface{}
}
func readUser(p *readUserParams) {
stmt.Query(p.Id, p.Phone, p.Type, p.Last, p.First)
// ...
}
readUser(&readUserParams{Id: 2})
readUser(&readUserParams{First: "John", Last: "Doe"})
英文:
You can construct your one statement by enumerating all the parameters with their placeholders and then you could pass nil
explicitly where you don't have the parameter value.
stmt, err := db.Prepare("SELECT read_user(_id := $1, _phone := $2, _type := $3, _last := $4, _first := $5)")
if err != nil {
// ...
}
stmt.Query(2, nil, nil, nil, nil) // result should be equivalent to `SELECT read_user(_id := 2)`
stmt.Query(nil, nil, nil, "Doe", "John") // result should be equivalent to `SELECT read_user(_first := 'John', _last := 'Doe')`
And if you want to have named parameters in Go as well, you can create a struct type to represent the parameters and a wrapper func that'll map that parameter type's fields into the query:
type readUserParams struct {
Id interface{}
Phone interface{}
Type interface{}
Last interface{}
First interface{}
}
func readUser(p *readUserParams) {
stmt.Query(p.Id, p.Phone, p.Type, p.Last, p.First)
// ...
}
readUser(&readUserParams{Id: 2})
readUser(&readUserParams{First: "John", Last:"Doe"})
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