Clojure从表中选择记录并将这些记录插入另一个表 [英] Clojure Selecting records from a table and inserting those records into another table

问题描述

我正在尝试将数据从另一个数据库插入一个数据库。我可以使用选择查询，但是无法将选择查询插入到其他数据库或表中。

I am trying to insert data into one database from a different database. I have the select query working but I haven't been able to take the select query and insert it into a different database and or table.

(jdbc/query db ["select * from employees
                    where employee_id = 1927"]
                {:as-arrays? true})

现在，如何将上述数据动态地插入到另一个表中？

Now, how do I now insert the above data into another table dynamically?

推荐答案

假设您的雇员表如下所示：

create table employees (
    employee_id integer,
    name        text,
    primary key (employee_id)
);
insert into employees (employee_id, name) values (123, 'taylor');

我不使用：as-arrays吗？对于该查询，则为true ，因为行映射查询在默认情况下会返回 。

I wouldn't use :as-arrays? true for the query, because the row maps query returns by default are easier to work with.

(jdbc/query db ["select * from employees where employee_id = ?" 123])
;; notice query parameterization; important! ----------------^  ^
=> ({:employee_id 123, :name "taylor"})

我们可以 def 供以后使用，首先假设 employee_id 是唯一的 结果，所以我的雇员将是一张地图（如果找不到，则为零）：

And we can def that for use later, taking the first result assuming employee_id is unique, so my-employee will be a single map (or nil if not found):

(def my-employee
  (first (jdbc/query db ["select * from employees where employee_id = ?" 123]))

现在让我们假设您要插入的另一个表看起来像这样：

Now let's assume your other table you want to insert into looks like this:

create table employees_too (
    employee_id integer,
    name        text,
    phone       text, -- just a new column
    primary key (employee_id)
);

然后您可以插入该员工行，如下所示：

Then you could insert that employee row like this:

(db/insert! conn "employees_too"
            (assoc my-employee
                   :phone (str (rand-int 9999999999))))
=> ({:employee_id 123, :name "taylor", :phone "250505207"})

，然后返回插入的行图（至少在使用PostgreSQL时）。

And the inserted row map(s) are returned (at least when using PostgreSQL).

您可能想为这些操作创建可重用的函数：

You may want to create reusable functions for these operations:

(defn get-employee [id]
  (first (db/query conn ["select * from employees where employee_id = ?" id])))
(defn employee->employee-too [employee]
  (assoc employee :phone (str (rand-int 99999))))
(defn insert-employee-too [employee-too]
  (db/insert! conn "employees_too" employee-too))

通过ID获取员工的功能，将员工行/映射转换为 other employees_too 表的架构，以及将行/映射插入该表的函数。您可以像这样将它们全部绑在一起：

A function to get an employee by ID, a function to transform an employee row/map into the other employees_too table's schema, and a function to insert a row/map into that table. You can tie them all together like this:

(-> (get-employee 123)
    (employee->employee-too)
    (insert-employee-too))
=> ({:employee_id 123, :name "taylor", :phone "8147"})

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