有什么方法可以使用 typescript ES6 类和模块连接 oracledb？

Question

我正在尝试使用 Typescript ES6 类模块实现 oracle 连接。

我已经安装了 @types/oracledb 包以及 oracledb 包。使用了 Jasmin 框架。

下面是我实现的代码。

import * as oracledb from 'oracledb';

export class ConnectionDAO{
/**
 * Connection Variable Declaration
 */
conn;

/**
 * Result Variable Declaration
 */
result;

/**
 *
 * Creates an instance of CommercialDAO.
 * To Initiate Connection and Make the connection utilized by @memberof CommercialDAO
 * @memberof CommercialDAO
 */
constructor() {
   this.conn = oracledb.getConnection({
        user: "commercial",
        password: "oracle",
        connectString: "localhost/COMMERCIALDB"
      }); 
}

public getRwCnt() {
    return new Promise(async function(resolve, reject) {
        try {
            let result = this.conn.execute('SELECT TESTCASEID FROM EXECUTE_TESTCASE');
            resolve(this.result.rows.length);
        } catch (err) { // catches errors in getConnection and the query
          reject(err);
        } 
        this.conn.release();
      });
}
}

错误：

TypeError: this.conn.execute is not a function

但是在这个代码连接中，它本身并没有被存储在 'this.conn' 变量中。

是否有避免承诺和异步功能？ 有没有其他解决方案可以实现这一目标？请为您提供有价值的解决方案和建议。期待样本 sn-p。

Answer 1

你的错误的真正原因

TypeError: this.conn.execute is not a function

是因为 this.conn 很可能是未定义的。添加这样的支票。

public getRwCnt() {
  if(this.conn === undefined){
    console.log("The connection is not ready yet.");
    return;
... // Rest of your function
}

但这只会突出你有问题，而不是告诉你原因。

原因是您的构造函数是严格同步的。 考虑有一个等待构造函数完成的函数。

这是一个有效的版本：

import * as OracleDB from 'oracledb';

export class ConnectionDAO {
  /**
   * Connection Variable Declaration
   */
  public conn: OracleDB.IConnection;
  public connProm: OracleDB.IPromise<void>;

  /**
   * Result Variable Declaration
   */
  result;

  /**
   *
   * Creates an instance of CommercialDAO.
   * To Initiate Connection and Make the connection utilized by @memberof CommercialDAO
   * @memberof CommercialDAO
   */
  constructor() {
    this.connProm = OracleDB.getConnection({
      user: "hr",
      password: "hr",
      connectString: "localhost/XEPDB1"
    }).then(async (connection: OracleDB.IConnection) => {
      console.log("Connection finally created in constructor")
      this.conn = connection;
    }).catch((err: any) => {
      console.error(err.message);
    });
    console.log(" - Dumping Connection state in the end of the constructor", {conn: this.conn} , {connProm: this.connProm} );
  }

  public getRwCnt() {
    let me = this;
    return new Promise(async function (resolve, reject) {
      try {
        console.log(" - Dumping Connection state BEFORE waiting",{conn: me.conn} , {connProm: me.connProm} );
        await me.connProm;
        console.log(" - Dumping Connection state AFTER waiting",{connServerVersion: me.conn.oracleServerVersion } , {connProm: me.connProm} );
        let result = await me.conn.execute('SELECT count(*) FROM employees');
        resolve(result.rows);
      } catch (err) { // catches errors in getConnection and the query
        console.log("[Error] happened? - calling reject",err);
        reject(err);
      }
      if(me.conn) // Only release it it if it actually is set
        me.conn.release();
    });
  }
}

const d = new ConnectionDAO();

d.getRwCnt()
  .then((result)=>{console.log("RowCount",result)})
  .catch((err)=>{console.error("Promise rejected - ",err)})

console.log("Object constructor returned");

用 ts-node 运行会得到这个结果

 - Dumping Connection state in the end of the constructor { conn: undefined } { connProm: Promise { <pending> } }
 - Dumping Connection state BEFORE waiting { conn: undefined } { connProm: Promise { <pending> } }
Object constructor returned
Connection finally created in constructor
 - Dumping Connection state AFTER waiting { connServerVersion: 1804000000 } { connProm: Promise { undefined } }
RowCount [ [ 107 ] ]

Answer 2

您似乎在函数getRwCnt() 中以错误的方式使用了this。

记住 JavaScript 中的每个函数都有自己的this。

选项1将顶部this分配给函数开头的另一个变量

public getRwCnt() {
    let me = this; 
    return new Promise(async function(resolve, reject) {
        try {
            let result = me.conn.execute('SELECT TESTCASEID FROM EXECUTE_TESTCASE');
            resolve(this.result.rows.length);
        } catch (err) { // catches errors in getConnection and the query
          reject(err);
        } 
        me.conn.release();
      });

选项 2 使用 ES6 箭头函数

public getRwCnt() {

        return new Promise(async (resolve, reject) => {
            try {
                let result = this.conn.execute('SELECT TESTCASEID FROM EXECUTE_TESTCASE');
                resolve(this.result.rows.length);
            } catch (err) { // catches errors in getConnection and the query
              reject(err);
            } 
            this.conn.release();
          });

Answer 3

我尝试了您的解决方案，但看起来 typescript 没有在等待调用 等待我.connectionPromise; 另外，不确定连接是否成功。我的输出低于输出。

Inside constructor
get Connection executed....
 - Dumping Connection state in the end of the constructor { conn: undefined } { connProm: Promise { <pending> } }
Inside getRowNumbers function call....
Connection state BEFORE waiting:  { conn: undefined } { connectionPromise: Promise { <pending> } }
Object constructor returned

Somehow below output lines in your code are missing for me.

Connection finally created in constructor
 - Dumping Connection state AFTER waiting { connServerVersion: 1804000000 } { connProm: Promise { undefined } }
RowCount [ [ 107 ] ]