如何使用 Angular Material Paginator 和连接到 SQL 数据库的节点 js 后端获取前端的文档计数？

Question

我目前正在尝试使分页器的逻辑正确。我已经到了返回文档并显示每页正确数量的文档的地步，但是我似乎无法让页数部分正常工作，它没有更新超过 0 的 0。我正在使用的数据库是带有sequelize的MySQL。

这是我以 html 文件开头的代码。

   <mat-paginator color="accent" [length]="totalBlogs" [pageSize]="blogsPerPage" 
  [pageSizeOptions]="pageSizeOptions" (page)="onChangedPage($event)" *ngIf="blogs.length > 0"> 
   </mat-paginator>

这是我使用分页器的组件中的代码。

totalBlogs = 0;
   blogsPerPage = 2;
   pageSizeOptions = [1, 2, 5, 10];
   currentPage = 1;

   


  constructor(
    private authService: AuthService,
    private blogService: BlogService
  ) { }

  ngOnInit() {
    this.isLoading = true;
    this.blogService.getBlogs(this.blogsPerPage, this.currentPage);
    this.userId = this.authService.getUserId();
    this.blogSubs = this.blogService.getBlogUpdateListener()
    .subscribe((blogData: { blogs: Blog[], blogCount: number}) => {
      this.isLoading = false;
      this.totalBlogs = blogData.blogCount;
      this.blogs = blogData.blogs;
    });
  }
  onChangedPage(pageData: PageEvent) {
    console.log(pageData);
    this.isLoading = true;
    this.currentPage = pageData.pageIndex + 1;
    this.blogsPerPage = pageData.pageSize;
    this.blogService.getBlogs(this.blogsPerPage, this.currentPage);
  }

服务文件的代码如下。

getBlogs(blogsPerPage: number, currentPage: number) {
    const queryParams = `?pagesize=${blogsPerPage}&page=${currentPage}`;
    this.http.get<{ message: string, blogs: any, maxBlogs: number}>(
      BACKEND + 'all/blogs/' + queryParams/* ,
      { headers: header } */
    ).pipe(map((blogData) => {
      return {
        blogs: blogData.blogs.map((blog: {
          id: string;
          title: string;
          description: string;
          date: string;
          author: string;
          user_id: string;
          is_deleted: string;
        }) => {
          return {
            id: blog.id,
            title: blog.title,
            description: blog.description,
            date: blog.date,
            author: blog.author,
            userId: blog.user_id,
            is_deleted: blog.is_deleted
          }
        }), maxBlogs: blogData.maxBlogs
      }
    })
    ).subscribe(transformedBlogsData => {
      this.blogs = transformedBlogsData.blogs;
      this.blogsUpdated.next({
        blogs: [...this.blogs],
        blogCount: transformedBlogsData.maxBlogs
      });
    });
  }

最后，当我加载带有分页器的页面时，在从 PageEvent 记录 pageData 时，我在控制台中得到以下信息。

Answer 1

首先，请澄清它的MS Sql 或 MY Sql，我假设它的MY Sql 给你一个示例。 其次，这不是一个文档数据库，它是一个关系/RDB，所以你会有一个行数或结果数。

---

Node JS 后端的计数

var mysql = require('mysql');
 
var connection = mysql.createConnection({
    host: 'localhost',
    user: 'root',
    password: '',
    database: 'yourDataBase',
    debug: false,
});
 
console.log("Connected to Mysql");
connection.connect();
 
var sql = "SELECT * FROM myBLogsTable";

var totalRows;
var totalPageCount;
 
var query = connection.query(sql, function(err, result) {
    // This is your total row/document count
    console.log("Total Records:- " + result.length);
    // here you can get the total results & page count, send this back to angular front end. Just make sure its not div/zero error.
    // totalPageCount = result.length/blogsPerPage;
});
 
connection.end();

---

回答您关于结果大小的问题

//use length For select query.
connection.query(sql, [x,y], function(err, results) {
    numRows = results.length;
});

//Use affectedRows for an CUD query.
connection.query(sql, [var1,var2], function(err, result) {
    numRows = result.affectedRows;
});

---

对于像这样来自here..的分页

router.get('/?', function(req, res, next) {
    const sql = "SELECT * from users ";
    const existingParams = ["title", "active"].filter(field => req.query[field]);
    const pageNum = req.query.p || 1;
    const pageSize = req.query.p_size || 100;


    if (existingParams.length) {
        sql += " WHERE ";
        sql += existingParams.map(field => `${field} = ?`).join(" AND ");
    }
    sql += ` LIMIT  ${(pageNum - 1) * PageSize},${PageSize}`;
    ...
});