shop-app | Android 旅游电商APP，景区介绍，特色商品购买，微信支付，支付宝支付 | SDK library

To fully take advantage of the Provider you already have setup, you should make the body of your scaffold a Consumer widget. Keep the same logic inside, but it would need to be based on a bool (initialized to true) that lives within the Orders class.

Some orders don't have products, for example:

The first thing is that your Scenario/result schema is probably lacking.

That is the Order to Product relationship should probably be a many-many relationship. That is many products can be referenced by many odrers. Such a relationships is typically handled by a reference table.

So you would have a Customer table, an Order table that has a column that references a Customer, a Product table that references nothing and a reference table that has two columns one to reference the product, the other to reference the product.

@ForeignKey defines a requirement that the column or columns used to reference/relate/associate must reference a value in the parent.

So say the Customer has a column (or columns that uniqeuly identifies the customer let's say 1 for one such Customer, 2 for another and so on. Then an Order would have a column that references the Customer for who the order is made (assuming an Order is per a Customer). Then The foreign key adds a constraint (rule) that requires that the value in the Order (The child) must be a value and exists in the referenced column of the Customer table (the parent). If an insert (new Order) or an update (of the Customer or the Order) or a deletion (of the Customer) results in this requirement then a conflict (error) will result.

An @ForeignKey can, to simplify maintaining the referential/relationship integrity, also include ON UPDATE and ON DELETE actions (CASCADE perhaps the most typically used option) taken when the Parent value is updated or deleted (CASCADE makes the change or deletion to the Parent's Children i.e. cascading the change to the children).

A Foreign key isn't required for such relationships but can assist.

@Embedded includes the fields (columns from a database persepective) of an Entity (or a Non-Entity class) to be included in a class or Entity.

@Reltionship allows related data (entities) to be extracted/included.

Consider the following Entities that define the tables (as per the suggested schema) :-

To resolve the issue please change the order of your code from,

TLDR

• Move the modules in devDependencies into the dependencies section
• Set the config variable NPM_CONFIG_PRODUCTION to false in the Heroku settings

Explanation

Heroku, in a attempt to reduce the bundle output of your project, does not install devDependencies when it is setting up your project.

The general rule of Node application development is that all modules that require do not contribute to the running of your application must go into your devDependencies and all the modules that do go into the dependencies

From the look of your package.json, you do not necessarily have to put anything in the devDependencies since popper and jQuery do belong in the dependencies section.

You can alternatively set the NPM_CONFIG_PRODUCTION variable in Heroku to false, however this is not the recommended approach, because this technically makes the app not a production application

This error means that you load the same dependency from two different urls. For instance

I came across the same question. I found out it's due to differences between Maven targets (e.g. dependency:resolve vs dependency:resolve-plugin). Basically, dependency:resolve is for application libraries, dependency:resolve-plugin is for plugin libraries. Hence, libraries are downloaded in both RUN steps.

dependency:resolve tells Maven to resolve all dependencies and displays the version. JAVA 9 NOTE: will display the module name when running with Java 9.

dependency:resolve-plugins tells Maven to resolve plugins and their dependencies.

https://maven.apache.org/plugins/maven-dependency-plugin/index.html

Even with dependency:resolve-plugins, Maven will not download all required libraries as package is a built-in target and requires additional libraries which dependency:resolve-plugin won't know to resolve in the first RUN. I also tried dependency:go-offline without success.

One solution is to run your build targets before and after adding your code to the build image. This will pull all the plugin dependencies into the lower layer allowing them to be re-used.

Applying this solution to your example above is as follows:

When do we need to call super()?

super() calls the constructor of the element's superclass (parent class). If an element's definition defines a class that extends another class and super() is not called explicitly, the element calls the constructor of the superclass by default.

When does this call need to be inside the constructor() function?

The proper place to call super() is inside the element's constructor() method.

And what are the consequences of not calling super() as appears in the case of the Shop app?

In the case where,