Is there a method for establishing a connection to oracledb using TypeScript ES6 class and module?

Question

Is there a method for establishing a connection to oracledb using TypeScript ES6 class and module?

My goal is to implement an Oracle connection using Typescript ES6 Class module. I have successfully installed the @types/oracledb package and oracledb package, with the Jasmin framework used in my project.

Below is the code I have implemented:


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();
      });
}
}

Error:

TypeError: this.conn.execute is not a function

The issue here is that the connection itself is not being stored in the 'this.conn' variable as expected.

I am looking for alternative solutions to achieve this without using promises and async functions. Any other suggestions on how to resolve this? Your valuable input and sample snippet would be greatly appreciated.

oracle typescript protractor es6-class

Answer 1

Answer №1

The main cause of the error you are facing:

TypeError: this.conn.execute is not a function

Occurs because 'this.conn' is most likely undefined. To address this issue, consider adding a check like the following:

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

However, simply spotting the problem won't provide you with the reason behind it.

The root cause lies in the fact that your constructor is entirely synchronous. You might want to introduce a function that waits for the constructor to complete its execution.

Here's an altered version that resolves this concern:

import * as OracleDB from 'oracledb';

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

  /**
   * Declaration of Result Variable
   */
  result;

  /**
   *
   * Initiates CommercialDAO - establishes and utilizes a connection 
   * @memberof CommercialDAO
   */
  constructor() {
    this.connProm = OracleDB.getConnection({
      user: "hr",
      password: "hr",
      connectString: "localhost/XEPDB1"
    }).then(async (connection: OracleDB.IConnection) => {
      console.log("Successfully created connection in constructor")
      this.conn = connection;
    }).catch((err: any) => {
      console.error(err.message);
    });
    console.log(" - Checking Connection state at end of constructor", {conn: this.conn} , {connProm: this.connProm} );
  }

  public getRwCnt() {
    let me = this;
    return new Promise(async function (resolve, reject) {
      try {
        console.log(" - Checking Connection state BEFORE waiting",{conn: me.conn} , {connProm: me.connProm} );
        await me.connProm;
        console.log(" - Checking 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] occurred? - calling reject",err);
        reject(err);
      }
      if(me.conn) // Release only if it has been 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("Constructor object returned");

If executed with ts-node, the following outcome is obtained:

 - Checking Connection state at end of constructor { conn: undefined } { connProm: Promise { <pending> } }
 - Checking Connection state BEFORE waiting { conn: undefined } { connProm: Promise { <pending> } }
Constructor object returned
Successfully created connection in constructor
 - Checking Connection state AFTER waiting { connServerVersion: 1804000000 } { connProm: Promise { undefined } }
RowCount [ [ 107 ] ]

Answer 2

The main cause of the error you are facing:

TypeError: this.conn.execute is not a function

Occurs because 'this.conn' is most likely undefined. To address this issue, consider adding a check like the following:

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

However, simply spotting the problem won't provide you with the reason behind it.

The root cause lies in the fact that your constructor is entirely synchronous. You might want to introduce a function that waits for the constructor to complete its execution.

Here's an altered version that resolves this concern:

import * as OracleDB from 'oracledb';

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

  /**
   * Declaration of Result Variable
   */
  result;

  /**
   *
   * Initiates CommercialDAO - establishes and utilizes a connection 
   * @memberof CommercialDAO
   */
  constructor() {
    this.connProm = OracleDB.getConnection({
      user: "hr",
      password: "hr",
      connectString: "localhost/XEPDB1"
    }).then(async (connection: OracleDB.IConnection) => {
      console.log("Successfully created connection in constructor")
      this.conn = connection;
    }).catch((err: any) => {
      console.error(err.message);
    });
    console.log(" - Checking Connection state at end of constructor", {conn: this.conn} , {connProm: this.connProm} );
  }

  public getRwCnt() {
    let me = this;
    return new Promise(async function (resolve, reject) {
      try {
        console.log(" - Checking Connection state BEFORE waiting",{conn: me.conn} , {connProm: me.connProm} );
        await me.connProm;
        console.log(" - Checking 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] occurred? - calling reject",err);
        reject(err);
      }
      if(me.conn) // Release only if it has been 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("Constructor object returned");

If executed with ts-node, the following outcome is obtained:

 - Checking Connection state at end of constructor { conn: undefined } { connProm: Promise { <pending> } }
 - Checking Connection state BEFORE waiting { conn: undefined } { connProm: Promise { <pending> } }
Constructor object returned
Successfully created connection in constructor
 - Checking Connection state AFTER waiting { connServerVersion: 1804000000 } { connProm: Promise { undefined } }
RowCount [ [ 107 ] ]

Answer 3

Answer №2

It appears that the this keyword is being misused in the function getRwCnt().

Remember, each function in JavaScript has its own this context.

Option 1: Assign the initial this value to another variable within the function:

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();
      });

Option 2: Utilize ES6 Arrow functions:

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 4

It appears that the this keyword is being misused in the function getRwCnt().

Remember, each function in JavaScript has its own this context.

Option 1: Assign the initial this value to another variable within the function:

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();
      });

Option 2: Utilize ES6 Arrow functions:

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 5

Answer №3

After implementing your recommended solution, I encountered an issue where TypeScript does not seem to be waiting for the call to await me.connectionPromise. Additionally, there is uncertainty regarding whether the connection was successful or not as indicated by the output below.

Upon investigating further, I discovered that the following lines were missing from your provided code snippet:

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

Answer 6

After implementing your recommended solution, I encountered an issue where TypeScript does not seem to be waiting for the call to await me.connectionPromise. Additionally, there is uncertainty regarding whether the connection was successful or not as indicated by the output below.

Upon investigating further, I discovered that the following lines were missing from your provided code snippet:

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

Answer 7

Answer №4

Encountered a similar problem. I solved it by updating my import statement:

import * as oracledb from 'oracledb';

to

import oracledb from 'oracledb';

This resolved the issue for me.

Answer 8

Encountered a similar problem. I solved it by updating my import statement:

import * as oracledb from 'oracledb';

to

import oracledb from 'oracledb';

This resolved the issue for me.

Is there a method for establishing a connection to oracledb using TypeScript ES6 class and module?

Answer №1

Answer №2

Answer №3

Answer №4

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