本文向您展示如何使用INSTEAD OF TRIGGER进行更新

1. 非版本视图
2. 非版本视图的嵌套表列

此INSTEAD OF触发器提供了一种修改views的方法，该views无法直接通过DML语句（如INSERT，UPDATE和DELETE）进行修改

INSTEAD OF触发器是

1. 始终是行级触发器。
2. 可以读取旧值和新值，但不能更改它们。
3. 不能是有条件的。 意味着我们不能添加WHEN或IF条件。

1.将数据插入视图

在此示例中，我们创建了一个INSTEAD OF触发器，当我们在视图上执行insert语句时，它将在view各个表中插入行。

1.1创建表。

CREATE TABLE customer_details
(customer_id number(10) primary key,customer_name varchar2(20),country varchar2(20)
);

CREATE TABLE projects_details
(project_id number(10) primary key,project_name varchar2(30),project_start_Date date,customer_id number(10) references customer_details(customer_id)
);

1.2创建customer_projects_view视图以获取客户及其项目的结果。

CREATE OR REPLACE VIEW customer_projects_view ASSELECT cust.customer_id, cust.customer_name, cust.country,projectdtls.project_id, projectdtls.project_name, projectdtls.project_start_DateFROM customer_details cust, projects_details projectdtlsWHERE cust.customer_id = projectdtls.customer_id;

1.3如果我们直接将INERT插入customer_projects_view视图，则数据库将引发以下错误：

INSERT INTO customer_projects_view VALUES (1,'XYZ Enterprise','Japan',101,'Library management',sysdate);-- output
SQL Error: ORA-01779: cannot modify a column which maps to a non key-preserved table
01779. 00000 -  "cannot modify a column which maps to a non key-preserved table"
*Cause:    An attempt was made to insert or update columns of a join view whichmap to a non-key-preserved table.
*Action:   Modify the underlying base tables directly.

1.4相反，我们应该在视图上创建INSTEAD OF触发器以执行实际操作。

CREATE OR REPLACE TRIGGER trg_cust_proj_view_insertINSTEAD OF INSERT ON customer_projects_viewDECLAREduplicate_info EXCEPTION;PRAGMA EXCEPTION_INIT (duplicate_info, -00001);BEGININSERT INTO customer_details(customer_id,customer_name,country)VALUES (:new.customer_id, :new.customer_name, :new.country);INSERT INTO projects_details (project_id, project_name, project_start_Date, customer_id)VALUES (:new.project_id,:new.project_name,:new.project_start_Date,:new.customer_id);EXCEPTIONWHEN duplicate_info THENRAISE_APPLICATION_ERROR (num=> -20107,msg=> 'Duplicate customer or project id');END trg_cust_proj_view_insert;

1.5再次插入视图。 INSTEAD OF触发器将被触发并将数据插入到实际表中。

INSERT INTO customer_projects_view VALUES (1,'XYZ Enterprise','Japan',101,'Library management',sysdate);INSERT INTO customer_projects_view VALUES (2,'ABC Infotech','India',202,'HR management',sysdate);

1.6选择表格。

SELECT * FROM customer_details;

SELECT * FROM projects_details;

1.7选择视图。

SELECT * FROM customer_projects_view;

2.嵌套表视图列

使用INSTEAD OF触发器将数据插入嵌套表视图列的示例。

2.1创建表，键入，嵌套表视图列进行测试。

CREATE TABLE vehicle_mfg_company_details (company_id number(10) primary key,company_name varchar2(50) NOT NULL
);

CREATE TABLE vehicle_details (vehicle_id  number(10) primary key,company_id  number(10) references vehicle_mfg_company_details(company_id),vehicle_model_name varchar2(50) NOT NULL
);

CREATE OR REPLACE TYPE nestedTableEle
IS
OBJECT (vehicle_id NUMBER(10),vehicle_model_name VARCHAR2(50));

-- nested table view column
CREATE OR REPLACE TYPE vehicle_details_list_ ISTABLE OF nestedTableEle;

2.2创建视图。

CREATE OR REPLACE VIEW company_vehicles_view ASSELECT company.company_id, company.company_name,CAST (MULTISET (SELECT vehicle.vehicle_id, vehicle.vehicle_model_nameFROM vehicle_details vehicleWHERE vehicle.company_id = company.company_id)AS vehicle_details_list_) vehiclelist
FROM vehicle_mfg_company_details company;

2.3将数据插入嵌套表视图列中。

-- no error.
INSERT INTO vehicle_mfg_company_details VALUES (101,'Ford');-- error
INSERT INTO TABLE (SELECT vw.vehiclelist FROM company_vehicles_view vwWHERE company_id = 101
)
VALUES (1, 'EcoSport');-- output
SQL Error: ORA-25015: cannot perform DML on this nested table view column
25015. 00000 -  "cannot perform DML on this nested table view column"
*Cause:    DML cannot be performed on a nested table view column except throughan INSTEAD OF trigger
*Action:   Create an INSTEAD OF trigger over the nested table view columnand then perform the DML.

2.4创建INSTEAD OF触发器

CREATE OR REPLACE TRIGGER trg_comp_vehicles_view_insrtINSTEAD OF INSERT ON NESTED TABLE vehiclelist OF company_vehicles_viewREFERENCING NEW AS VehiclePARENT AS CompanyFOR EACH ROW
BEGIN-- Insert on nested table translates to insert on base table.INSERT INTO vehicle_details (vehicle_id,company_id,vehicle_model_name)VALUES (:Vehicle.vehicle_id,:Company.company_id,:Vehicle.vehicle_model_name);
END;

2.5再次将数据插入嵌套表视图列。

INSERT INTO TABLE (SELECT vw.vehiclelist FROM company_vehicles_view vwWHERE company_id = 101
)
VALUES (1, 'EcoSport');INSERT INTO TABLE (SELECT vw.vehiclelist FROM company_vehicles_view vwWHERE company_id = 101
)
VALUES (2, 'Endeavour');

2.6显示表。

select * from vehicle_mfg_company_details;

select * from vehicle_details;

参考文献

1. 代替OF触发器：-Oracle官方文档
2. PL / SQL触发器：-Oracle官方文档
3. Oracle PL / SQL – UPDATE触发器之前的示例

翻译自: https://mkyong.com/oracle/oracle-plsql-instead-of-trigger-example/