• Database standardization design


    Abnormal operation Modify exception, insert exception, delete exception Data dependence The connection between data Functional dependence FD Attribute is the most basic data dependency If x is determined, thenThe only definite yY is said to depend on X, X – > y If X – > y and Y is a subset of X, it […]

  • Data structure and algorithm learning — Set


    aggregate Almost every language has a set structure. A set is usually composed of a group of unordered and unrepeatable elements; in a computer, the elements in the structure usually identified by a set are not allowed to be repeated. You can also think of a set as a special array. The special thing is […]

  • Mongo database learning


    Chapter 2. Basic knowledge of mongodb 1 documentation A document is equivalent to a row in a relational database. The key value pairs in the document are ordered. 2 set A set is equivalent to a table. 2.1 dynamic mode Suppose a field named “type” in the collection is used to indicate whether the document […]

  • How to encapsulate a flexible and highly reusable Vue framework?


    preface:In general, when we create Vue projects, we use the official vue-cli2 scaffold to build projects. Generally speaking, projects created in this mode do not need too much configuration. However, there is a pain point that every project needs to be rebuilt and configured. Is there a way to save these tedious processes? For example, […]

  • Mongoengine + Flash Development tips (1)


    1. The data model class refers to itself, such as a list of people who are concerned carelist = ListField(ReferenceField(‘self’)) 2. Query the reference field. The reference field can only query the objectid, and other fields cannot be queried, unless the objectid of the target object is found first, and then the reference field is […]

  • An analysis of the problem of outer margin merging


    The outer margin merging problem mainly occurs in the presentation of the upper outer margin problem: When both the parent set and the subset are margin top, one is 50px and the other is 20px. SelectThe biggest valueWhat’s the reason why the subset can’t achieve margin top = > due to the merging of parent-child […]

  • Tensorflow learning notes (11): data operation guide


    Introduction To do a machine learning project with tensorflow, you need to have a variety of code capabilities: Engineering development capability: how to read data, how to design and run computation graph, how to save and restore variables, how to save statistical results, how to share variables, how to deploy in a distributed way Data […]

  • Collection of front-end data structures


    Set, dictionary, hash table also known as hash table Collections, dictionaries, and hash tables can store values that do not repeat. In a collection, we are interested in each value itself and treat it as the primary element. In the dictionary, we store data in the form of [key, value]. The same is true in […]

  • All subsets of list generated by python (no recursion and no introduction of standard library)


    Without recursion and standard library, all subsets of a list can be obtained by two for loops L = [1, 2, 3, 4] List = [[]] For I in range (len (L)): (fixed length) For J in range (len (list)):         sub_List = List[j] + [L[i]]         if sub_List not in L:             List.append(sub_List) print(‘List =’, List) Main ideas: All elements in the variable length list will be repeatedly traversed until the fixed length L […]

  • When the first load data occurs, the value does not take effect immediately


    Requirement: get the current value directly at each level of selection (and load the subset dynamically) There was a problem: the value did not change immediately when the subset was first loaded. @The on change event also did not listen for changes. For example: Code monitoring:Callback method: Load subset Solution: modify the value manually All […]

  • JQuery add input box dynamically


    There are two ways for jQuery to dynamically add input boxes. 1. Display page <!DOCTYPE html> <html lang=”en”> <head> <meta charset=”UTF-8″> <meta http-equiv=”X-UA-Compatible” content=”IE=edge”> <meta name=”viewport” content=”width=device-width, initial-scale=1″> < title > dynamically add input box < / Title > <!–<link href=”assets/font-awesome/css/font-awesome.css” rel=”stylesheet” />–> <!–[if lt IE 9]> <script></script> <script></script> <![endif]–> </head> <body> <h1>Add input box […]

  • Leetcode’s HOT100 series — 17. Letter combination of telephone number — Application of another idea of backtracking


    When submitting leetcode, I encountered a problem. I always said that the access was out of bounds, but I checked it carefully n times, but I couldn’t find it.Because I use the count global variable, the addition indicates the current array access location,Later, it suddenly occurred to me that when leetcode was running test cases, […]