Shulou(Shulou.com)06/01 Report--

Mongodb is very suitable for doing this, the call to api only uses the entry-level CRUD, the idea is clear, and the coding will be smooth, so you will find that I have said more in this blog than coding.

The expected function of the comment list

Just like StackOverFlow, users can send their own questions and other users can answer them. at the same time, landlords can reply to other people's comments, and others can still reply to landlords.

Data structure

Mongodb can store documents. In fact, all we have to do is build a suitable class, and the comment gang will be more than half successful.

The entity of the question / comment is as follows

problem

Public class Problem implements Serializable {@ Idprivate String _ id;// keyprivate String nickname; / / username private String avator; / / user profile private String userId; / / user name idprivate String title; / / title private String content; / / content private boolean answered; / / whether private Date createTime has been answered; / / creation time private boolean flag = false; / / whether the tag is me. Default is the answer list of non-personal private List answerList; / / questions.

Comment

Public class Answer {private String id;// 's current answer uniquely identifies the private String nickname; / / username private String avator; / / the user's avatar private Integer userId; / / the id private String Content of the user who answered; / / the content of the answer private Date time; private boolean flag = false;// default false. Not the mark of my private Integer group; / / grouping}

Train of thought

In the Answer entity, a collection is not added to store entities of Answer type. If you add this collection, it is really a good idea. There are other people's replies to you in the reply, which is a natural tree structure. However, considering the difficulty of front-end rendering, this scheme is abandoned.

A collection of answered entity classes is maintained in the entity class of the question, in which all the examples of answers to the building master's questions are placed, including the building master's reply to the question respondent and the respondent's reply to the question.

So there are only two layers in this way, and all responses to this question are maintained in one question, and the difficulty of front-end rendering is greatly reduced, but then something happens.

What does the back end do when the user queries the details of a question?

When the user queries the details of a question, the back end takes the id of the question and fetches the instance of the question from the database, and then processes the Answer collection, grouping the collections sorted by time according to the way we specify, and then sorting them by time.

What is the grouping?

At that time, it was grouped according to different users, all the comments of the same user, the responses of the landlord to it, and the responses of others to it were all put together, so we needed a field, group (my chosen user id), to store the logo of the grouping. The instances in the group are sorted by time, so that the overall hierarchy is divided.

Public JsonResult problemDetail (@ PathVariable String problemId) {Optional byId = problemRepository.findById (problemId); if (! byId.isPresent ()) {return JsonResult.fail ("you did not get the details page, please contact the administrator");} Problem problem = byId.get (); if (problem.getAnswerList (). Size () > 0) {Map collect = problem.getAnswerList () .stream (Collectors.groupingBy (Answer::getGroup)) ArrayList list = new ArrayList (); collect.forEach ((KMagnev)-> {list.addAll (v);}); problem.setAnswerList (list);} return JsonResult.ok ("return details Page" + problem);}

Locate the current user's comments

If the front end wants to show its own comments and other people's comments in the left and right parts of the page, it needs a tag. Since the above is already traversing, it might as well add one more judgment. Compare the user id submitted by the front end with the userId in Answer. If it is equal, mark the flag of the comment as true, and the front end distinguishes according to this tag, thus giving users more permissions, such as deleting their own comments.

Limitation

If there are no questions like NetEase's music, with tens of thousands of comments, it is estimated that they will be invalidated. Although it will be fast to use stream, it will not be able to handle the quantity, but if the number is small, it is still acceptable. In fact, the ideal state is that comments can be obtained in the form of pagination, which feels authentic.

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