Firebase:如何从存储特定密钥的数据中检索记录？

我在firebase中有数据如下所示:

"application": {
  "companies": {
    "firebase": {
      "creation": {
        "name": "Firebase Inc",
        "location": "USA"
      },

      "google": {
        "creattion": {
          "name": "Google Inc",
          "location": "USA"
        }
      }

      "facebook": {
      },

      "apple": {
      }
    }
  }
}

companies密钥下有成千上万的记录.我如何有效地执行以下查询？

如何仅查询creation其名称下存在密钥的记录？

如何只查询creation名称下没有密钥的记录？

我还想调用.on('child_added')返回的结果集,以便稍后我只能处理那些特定的记录.可能吗？

编辑:更简单的方式,而无需使用额外的参数

查询

以下是无需使用额外参数即可执行此操作的查询:

找到没有 的公司creation:

var ref = new Firebase(fbUrl+'/companies').orderByChild("creation").equalTo(null);

找到公司用 creation:

var ref = new Firebase(fbUrl+'/companies').orderByChild("creation").startAt(!null);

您将添加".indexOn": "creation"规则.

编辑2:我很好奇,所以我把11,000条记录推到了/companies2(一半有creation孩子,有一半没有).我可以使用上面的查询(或我在下面显示的变体之一)在~4秒内检索5500个匹配记录.

编辑3:如果您经常运行这些查询,那么/companies根据存在的情况将孩子分成两个箱子可能是值得的creation.这样,您可以单独阅读这两个段,而无需依赖查询.

厂

这是修改后的工厂的样子(我修改了PLNKR以匹配):

app.factory("CompaniesFactory",function($q, fbUrl){
  return function(hasCreation){
    var deferred = $q.defer();
    var ref = new Firebase(fbUrl+'/companies').orderByChild("creation");
    var query;
    if (hasCreation) {
      query = ref.startAt(!null);
      // or: 
      // query = ref.startAt(true);
    } else {
      query = ref.equalTo(null);
      // or:
      // query = ref.endAt(!null);
      // query = ref.endAt(true);
    }
    query.once("value", function(dataSnapshot){
      deferred.resolve(dataSnapshot.val());
    }, function (error) {
      deferred.reject(error);
    });
    return deferred.promise;
  }
});

{
  "company1" : {
    "creation" : {
      "name" : "company1"
    },
    "hasCreation" : true
  },
  "company2" : {
    "name" : "company2"
  },
  "company3" : {
    "name" : "company3"
  },
  "company4" : {
    "creation" : {
      "name" : "company4"
    },
    "hasCreation" : true
  }
}

  "so:29179389":{
    ".read" : true,
    ".write" : true,
    "companies" : {
      ".indexOn" : "hasCreation"
    }
  }

app.factory("CompaniesFactory",function($q, fbUrl){
  return function(hasCreation){
    var deferred = $q.defer();
    if (!hasCreation) {
      hasCreation = null;
    }
    var ref = new Firebase(fbUrl+'/companies').orderByChild("hasCreation").equalTo(hasCreation);
    ref.once("value", function(dataSnapshot){
      deferred.resolve(dataSnapshot.val());
    });
    return deferred.promise;
  }
});

app.controller('HomeController',function($scope,fbUrl,CompaniesFactory) {
 $scope.getCompanies = function(hasCreation) {
  var companies = new CompaniesFactory(hasCreation).then(function(data){
     console.log(data);
     $scope.companies = data;
   });
 }
});

  

    Find with creation
    Find without creation
    
Companies:
    {{companies}}