Question

我是NodeJS和数据库的新手。我对程序的行为感到困惑。我只是试图创建表，然后将其删除。但是我的代码出了点问题。结果真的很奇怪。我运行了几次代码，结果却不同。结果示例：

First execution
[ { name: 'first' } ]
createTable error SQLITE_ERROR: table first already exists
[ { name: 'first' } ]
table first dropped

Second execution
[]
[]
table first(name text) created succesfully

Third execution
createTable error SQLITE_ERROR: table first already exists
[ { name: 'first' } ]
[ { name: 'first' } ]
table first dropped

下面列出的代码。如果有人可以指出我的错误，我将不胜感激。

import { Database } from 'sqlite3';

class DBWrapper {
    private db: Database;
    constructor(dbName: string) {
        this.db = new Database(dbName, (error) => {
            if (error) {
                console.log('Database construction failed');
            } else {
                console.log('Database created successfully');
            }
        });
    }

    public createTable(tableName: string): void {
        this.db.serialize(() => {
            this.db.run('CREATE TABLE ' + tableName, (error) => {
                if (error) {
                    console.log('createTable error ' + error.message);
                } else {
                    console.log('table ' + tableName + ' created succesfully');
                }
            });
        });
        this.db.close();
        this.db = new Database('sqlitest');
    }

    public printTables(): void {
        this.db.serialize(() => {
            this.db.all('select name from sqlite_master where type=\'table\'', (error, tables) => {
                console.log(tables);
            });
        });
        this.db.close();
        this.db = new Database('sqlitest');
    }

    public clear(): void {
        this.db.serialize(() => {
            this.db.all('select name from sqlite_master where type=\'table\'', (error, tables) => {
                if (error) {
                    console.log('error in select all tables');
                } else {
                    tables.forEach((table) => {
                        this.db.run('DROP TABLE ' + table.name, (innerError) => {
                            if (innerError) {
                                console.log('drop table ' + table.name + ' error ' + innerError.message);
                            } else {
                                console.log('table ' + table.name + ' dropped');
                            }
                        });
                    });
                }
            });
        });
        this.db.close();
        this.db = new Database('sqlitest');
    }
}

const testDB = new DBWrapper('sqlitest');
testDB.createTable('first(name text)');
testDB.printTables();
testDB.clear();
testDB.printTables();

Answer 1

在开始下一个命令之前，您需要等待每个命令完成。

通常，db.serialize()会为您执行此操作，但是您将在每个命令之后创建一个新的db实例，而该命令不知道前一个实例的挂起操作。

您应该重用db实例。

NodeJS中SQLite中的竞争条件

1 个答案: