relational-database | 易学教程

Can't get Laravel associate to work

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问题 I'm not quite sure if I understand the associate method in Laravel. I understand the idea, but I can't seem to get it to work. With this (distilled) code: class User { public function customer() { return $this->hasOne('Customer'); } } class Customer { public function user() { return $this->belongsTo('User'); } } $user = new User($data); $customer = new Customer($customerData); $user->customer()->associate($customer); I get a Call to undefined method Illuminate\Database\Query\Builder:

Entity Framework database mapping relationships (Duplicate creation using Seed() method)

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I created a post with an issue and another issue . These can be looked at for references but i consider them as handled. My question arising from these issues and the action i (need or not need) to apply bothers me because i don't quite understand EF its behavior and expectations. I have a Product, PurchasePrice and SalesPrice entity where my initial thought was that 1 Product can have multiple PurchasePrices but that 1 PurchasePrice only can exist in 1 Product (same for SalesPrice). Therefore these relations: // NOTE that BaseEntity just has a "int ID" prop and datetimes/stamps public class

MySQL second auto increment field based on foreign key

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I've come across this problem numerous times but haven't found a "MySQL way" to solve the issue as such - I have a database that contains users and reports . Each report has an id which I display as a report number to my users. The main complaint is that users are confused as to why reports have gone missing from their system. This is not actually the case. It is actually that they are recognizing a gap between their IDs and assume that these are missing reports, when in actual fact, it is simply becasue another user has filled in this auto-incrementing gap. I need to know if there is a way to

Can a database attribute be primary and foreign key?

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问题 I have 2 tables, User and Employee . Each user is given a User_ID and that is a primary key in the User table and a foreign key in the Employee table. Can that attribute in the Employee table also be a primary key? 回答1: If you have a one-to-one relation between two tables, then the primary key of the details table is a foreign key as well. master detail (1 : 1) +----------+ 1:1 +-------------+ | PK id |<---o| PK FK id | +----------+ +-------------+ | col1 | | col1 | | col2 | | col2 | | etc. |

Duplicating records to fill gap between dates

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问题 I need to do something really weird, which is to create fake records in a view to fill the gap between posted dates of product prices. Actually, my scenario is a little bit more complicated than that, but I've simplified to products/dates/prices. Let's say we have this table: create table PRICES_TEST ( PRICE_DATE date not null, PRODUCT varchar2(13) not null, PRICE number ); alter table PRICES_TEST add constraint PRICES_TEST_PK primary key (PRICE_DATE, PRODUCT); With these records: insert into

One-to-Many relationship in MySQL - how to build model?

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问题 I have got two tables: 1) Area 2) Map Each Area shall have at least 1 Map, but can also have more than one Map. One Map can only belong to one Area. How to build this in MySQL? 回答1: Add a Foreign key in Map that references the Area's Primary Key. That will enforce a one-to-many relationship between Maps and Areas. As for enforcing a minimum of one map per area (if that is necessary) there are some ideas in this post here. One of the simpler solutions would be to create a view that only

what are the advantages of defining a foreign key

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问题 What is the advantage of defining a foreign key when working with an MVC framework that handles the relation? I'm using a relational database with a framework that allows model definitions with relations. Because the foreign keys are defined through the models, it seems like foreign keys are redundant. When it comes to managing the database of an application in development, editing/deleting tables that are using foreign keys is a hassle. Is there any advantage to using foreign keys that I'm

How to perform a LEFT JOIN in SQL Server between two SELECT statements? [closed]

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问题 This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center. Closed 7 years ago . I have two SELECT statements in SQL Server like these: (SELECT [UserID] FROM [User]) (SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043) I

MySQL table with a varchar column as foreign key

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I am trying to create a table with a varchar column as foreign key but MySql gives me an error while creating the table. My query is like this: CREATE TABLE network_classes ( id TINYINT(1) UNSIGNED NOT NULL AUTO_INCREMENT, category VARCHAR(80) NOT NULL, PRIMARY KEY(id), KEY `key_1` (`id`,`category`) ) ENGINE=InnoDB; CREATE TABLE networks ( id TINYINT(3) UNSIGNED NOT NULL AUTO_INCREMENT, name VARCHAR(100) NOT NULL, category VARCHAR(80) NOT NULL, director_id TINYINT(3) UNSIGNED NULL, director_name VARCHAR(100) NULL, description VARCHAR(1000) NULL, last_modified TIMESTAMP NULL DEFAULT CURRENT

How to implement total disjoint specialization in database?

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Say there is a database for students and professors (a very simple one) and the relational database is the following: GradStudent (_id_, name, gradStuff) UndergradStudent (_id_, name, underGradStuff) Professor (_id_, name) Teaches(_prof_id_, _stud_id_) Considering that the relational database above is meant to represent total disjoint specialization, i.e. there is no table Student but rather two completely seperate ones, when writing this in SQL in order to implement the database, how would I fetch the student id for the Teaches table? I cannot figure out how to make a foreign key from two