loopbackjs:将模型附加到不同的数据源

问题描述

我定义了几个模型，这些模型在我的环境中使用数据源"db"(mysql).

I have defined several models that use a Datasource "db" (mysql) for my environment.

有什么办法可以将多个数据源附加到那些模型上，这样我就可以对不同的数据库执行REST操作?

Is there any way to have several datasources attached to those models, so I would be able to perform REST operations to different databases?

即: GET/api/Things?ds ="db"

i.e: GET /api/Things?ds="db"

获取/api/Things?ds ="anotherdb"

GET /api/Things?ds="anotherdb"

获取/api/Things(将使用默认ds)

GET /api/Things (will use default ds)

推荐答案

如上面@superkhau所述，每个LoopBack模型只能附加到单个数据源.

As @superkhau pointed above, each LoopBack Model can be attached to a single data-source only.

您可以为要使用的每个数据源创建(子类)新模型.然后，您可以通过唯一的REST URL公开这些按数据源的模型，也可以实现包装器模型，该包装器将方法分配给正确的特定于数据源的模型.

You can create (subclass) a new model for each datasource you want to use. Then you can either expose these per-datasource models via unique REST URLs, or you can implement a wrapper model that will dispatch methods to the correct datasource-specific model.

在我的示例中，我将展示如何为附加到db和anotherdb的Car模型公开每个数据源模型. Car模型以通常的方式通过common/models/car.json和common/models/car.js定义.

In my example, I'll show how to expose per-datasource models for a Car model that is attached to db and anotherdb. The Car model is defined in the usual way via common/models/car.json and common/models/car.js.

现在您需要定义每个数据源模型:

Now you need to define per-datasource models:

// common/models/car-db.js
{
  "name": "Car-db",
  "base": "Car",
  "http": {
    "path": "/cars:db"
  }
}

// common/models/car-anotherdb.js
{
  "name": "Car-anotherdb",
  "base": "Car",
  "http": {
    "path": "/cars:anotherdb"
  }

}

// server/model-config.json
{
  "Car": {
    "dataSource": "default"
  },
  "Car-db": {
    "dataSource": "db"
  },
  "Car-anotherdb": {
    "dataSource": "anotherdb"
  }
}

现在您可以使用以下URL:

Now you have the following URLs available:

GET /api/Cars:db
GET /api/Cars:anotherdb
GET /api/Cars

上面概述的解决方案有两个局限性:您必须为每个数据源定义一个新模型，并且无法使用查询参数选择该数据源.

The solution outlined above has two limitations: you have to define a new model for each datasource and the datasource cannot be selected using a query parameter.

要解决此问题，您需要使用其他方法.我再次假设已经定义了Car模型.

To fix that, you need a different approach. I'll again assume there is a Car model already defined.

现在您需要创建一个调度程序".

Now you need to create a "dispatcher".

// common/models/car-dispatcher.json
{
  "name": "CarDispatcher",
  "base": "Model", //< important!
  "http": {
    "path": "/cars"
  }
}

// common/models/car-dispatcher.js
var loopback = require('loopback').PersistedModel;
module.exports = function(CarDispatcher) {
  Car.find = function(ds, filter, cb) {
    var model = this.findModelForDataSource(ds);
    model.find(filter, cb);
  };

  // a modified copy of remoting metadata from loopback/lib/persisted-model.js
  Car.remoteMethod('find', {
    isStatic: true,
    description: 'Find all instances of the model matched by filter from the data source',
    accessType: 'READ',
    accepts: [
     {arg: 'ds', type: 'string', description: 'Name of the datasource to use' },
     {arg: 'filter', type: 'object', description: 'Filter defining fields, where, orderBy, offset, and limit'}
    ],
    returns: {arg: 'data', type: [typeName], root: true},
    http: {verb: 'get', path: '/'}
  });

  // TODO: repeat the above for all methods you want to expose this way

  Car.findModelForDataSource = function(ds) {
    var app = this.app;
    var ds = ds && app.dataSources[ds] || app.dataSources.default;

    var modelName = this.modelName + '-' + ds;
    var model = loopback.findModel(modelName);
    if (!model) {
      model = loopback.createModel(
        modelName,
        {},
        { base: this.modelName });
    }

    return model;
  };
};

最后一点是删除Car并在模型配置中使用CarDispatcher:

The final bit is to remove Car and use CarDispatcher in the model config:

// server/model-config.json
{
  "CarDispatcher": {
    dataSource: null,
    public: true
  }
}

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