database-relations

mysql many to many relationship

由 耗尽温柔 提交于 2019-12-14 01:43:46
问题 Been reading the tutorial How to handle a Many-to-Many relationship with PHP and MySQL . In this question I refer to the "Database schema" section which states the following rules: This new table must be constructed to allow the following: * It must have a column which links back to table 'A'. * It must have a column which links back to table 'B'. * It must allow no more than one row to exist for any combination of rows from table 'A' and table 'B'. * It must have a primary key. Now it's

Laravel Querying Relations Model::has('relation') doesn't work

由 谁都会走 提交于 2019-12-12 10:56:24
问题 In the Laravel documentation it says you can use this syntax for querying an object relation to get only the Posts that have at least one Comment: $posts = Post::has('comments')->get(); I'm trying something similar where I want to fetch only objects that have at least one relation object. These are my two classes: class Movie extends Eloquent { protected $table = 'movie'; public function matches() { return $this->hasMany("Match"); } } class Match extends Eloquent { protected $table = 'match';

Issue with Entity Framework/db relations

由 二次信任 提交于 2019-12-12 01:54:15
问题 I have a class Article: public class Article { public int Id { get; set; } public string Text { get; set; } public Title Title { get; set; } } And Title: public class Title { public int Id { get; set; } public string Name { get; set; } public int MaxChar { get; set; } } Before you can write an Article , you have to choose your Title from a list, so your StringLength for Article.Text can be determined. Meaning, this article can only have a certain amount of chars, deppending on what 'Title'

How to preserve data integrity in circular reference database structure?

由 拟墨画扇 提交于 2019-12-11 17:42:45
问题 I have looked at some DataBase normalisation and design methods to properly structure data and have read that circular referencing is not optimal as it jeopardises data integrity. I have a data structure in which I am unable to figure out how to eliminate a circular reference or to ensure that no faulty references are introduced. Database requirements: Each type of fruit requires fruit specific attributes A fruit delivery requires a fruit type which it contains A delivery of fruit needs to

Implementing foreign key type relationships in XSD schema

由 巧了我就是萌 提交于 2019-12-10 09:41:55
问题 I'm trying to wrap my head around xml schemas and one thing I'm trying to figure out is how to do relational type schemas where on element refers to another, possibly in another schema altogether. I've looked at the xsd:key and xsd:keyref and it seems like the sort of thing I'm interested in, but I'm not sure. Initially I just set attributes with the type xs:ID abd xs:IDREF, which obviously doesn't necessarily refer to a specific element as far as I could tell. Basically, I have several

How can I update hasandbelongstomany relations for multiple models at once in strongloop loopback

由 断了今生、忘了曾经 提交于 2019-12-07 15:22:22
问题 I have 2 models in a Strongloop Loopback API Products Tags Between those 2 models I have defined a hasAndBelongsToMany-relation . In my CMS I want a bulk-update functionality for my products, in which I can select many Products, and assign many tags, in one action. How can I save those easily to my Mysql-DB, without having to iterate over each product, then iterate over each tag, and link those 2 ? I checked in the docs and found the add and remove functions, but those only connect one model

How can I make and enforce a generic OneToOne relation in django?

由 别等时光非礼了梦想. 提交于 2019-12-07 06:08:58
问题 I'd like the exact same thing as django.contrib.contenttypes.generic.GenericForeignKey , but OneToOne instead of ForeignKey . I thought an easy (albeit marginally inelegant) workaround was to add unique=True to the field in question, but that borks. 回答1: Use unique_together ? Any combination of the content_type field and the ID field is a unique identifier for one object, therefore 1 to 1. http://docs.djangoproject.com/en/dev/ref/models/options/#unique-together 来源： https://stackoverflow.com

database model for products and product package with different combinations

由 偶尔善良 提交于 2019-12-06 07:19:35
问题 How would you design your database to achieve this functionality? Consider a scenario where we want to create a product relation (package) ... Say that we create a ProductTbl prod_id prod_name prod_fee 1 prepaid-A 19 usd 2 prepaid-B 29 usd 3 prepaid-C 39 usd 4 internet 9 usd 5 mms 1 usd 6 email 3 usd We want to offer a product package that provides better fees for customer. E.g. if customer choose prepaid-A + internet + mms they will have a pkg fee by 25 usd (instead of 29 usd). DESIGN A pkg

Implementing foreign key type relationships in XSD schema

由 痞子三分冷 提交于 2019-12-05 20:29:49
I'm trying to wrap my head around xml schemas and one thing I'm trying to figure out is how to do relational type schemas where on element refers to another, possibly in another schema altogether. I've looked at the xsd:key and xsd:keyref and it seems like the sort of thing I'm interested in, but I'm not sure. Initially I just set attributes with the type xs:ID abd xs:IDREF, which obviously doesn't necessarily refer to a specific element as far as I could tell. Basically, I have several different xml files where elements refer to other elements either in the same file or other files. It looks

How can I make and enforce a generic OneToOne relation in django?

由 白昼怎懂夜的黑 提交于 2019-12-05 09:38:02
I'd like the exact same thing as django.contrib.contenttypes.generic.GenericForeignKey , but OneToOne instead of ForeignKey . I thought an easy (albeit marginally inelegant) workaround was to add unique=True to the field in question, but that borks. Use unique_together ? Any combination of the content_type field and the ID field is a unique identifier for one object, therefore 1 to 1. http://docs.djangoproject.com/en/dev/ref/models/options/#unique-together 来源： https://stackoverflow.com/questions/4893823/how-can-i-make-and-enforce-a-generic-onetoone-relation-in-django
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