如何在没有循环依赖的情况下使用环回4实现链接模型 [英] How to implement chained models with loopback 4 without getting a Circular dependency

问题描述

当模型具有循环依赖性时，回送会报告错误。我正在寻找一种无需更改模型即可解决此问题的方法。

When models have circular dependencies Loopback reports an error. I am looking for a way to solve the issue without changing the models.

如果模型与自身相关，则解决方案似乎正在使用Getter.fromValue（）。但是，当关系通过多个模型循环时，此解决方案似乎不太有用。

If a model relates to itself the solution seems to be using Getter.fromValue(). However, when relations are circular through more models this solution seems not so usefull.

一个具有三个模型A，B和C的示例。让我们假设A引用B ，B引用C，而C引用A。然后，按照LB4文档，存储库将如下所示：

An example with three models A, B, and C. Let us assume that A references B, B references C, and C references A. Then the repositories would look like this when following the LB4 documentation:

Repository A:
constructor(
@repository(BRepo) private bGetter: Getter<BRepo>,
...

Repository B:
constructor(
@repository(CRepo) private cGetter: Getter<CRepo>,
...

Repository C:
constructor(
@repository(ARepo) private aGetter: Getter<ARepo>,
...

但这会导致循环依赖项失败。因此，问题是-如何在不更改模型依赖性的情况下解决此问题。

But this leads to a circular dependency failure. So the question is - how to fix this without changing the model dependencies.

推荐答案

该解决方案似乎将存储库绑定为Singletons

The solution seems to be binding the repositories as Singletons

@bind({scope: BindingScope.SINGLETON})
export class Repository ...

默认绑定是Transient，它会触发循环依赖项检查。

Default binding is Transient which triggers the circular dependency check.

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