HTML5本地存储——IndexedDB（二：索引）

在HTML5本地存储——IndexedDB（一：基本使用）中介绍了关于IndexedDB的基本使用方法，很不过瘾，这篇我们来看看indexedDB的杀器——索引。

熟悉数据库的同学都知道索引的一个好处就是可以迅速定位数据，提高搜索速度，在indexedDB中有两种索引，一种是自增长的int值，一种是keyPath：自己指定索引列，我们重点来看看keyPath方式的索引使用.

创建索引

我们可以在创建object store的时候指明索引，使用object store的createIndex创建索引，方法有三个参数

索引名称
索引属性字段名
索引属性值是否唯一

function openDB (name,version) {var version=version || 1;var request=window.indexedDB.open(name,version);request.onerror=function(e){console.log(e.currentTarget.error.message);};request.onsuccess=function(e){myDB.db=e.target.result;};request.onupgradeneeded=function(e){var db=e.target.result;if(!db.objectStoreNames.contains('students')){var store=db.createObjectStore('students',{keyPath: 'id'});store.createIndex('nameIndex','name',{unique:true}); store.createIndex('ageIndex','age',{unique:false}); }console.log('DB version changed to '+version);};}

这样我们在students 上创建了两个索引

利用索引获取数据

function getDataByIndex(db,storeName){var transaction=db.transaction(storeName);var store=transaction.objectStore(storeName);var index = store.index("nameIndex");index.get('Byron').onsuccess=function(e){var student=e.target.result;console.log(student.id);}}

这样我们可以利用索引快速获取数据，name的索引是唯一的没问题，但是对于age索引只会取到第一个匹配值，要想得到所有age符合条件的值就需要使用游标了

游标

在indexedDB中使用索引和游标是分不开的，对数据库熟悉的同学很好理解游标是什么东东，有了数据库object store的游标，我们就可以利用游标遍历object store了。

使用object store的openCursor()方法打开游标

function fetchStoreByCursor(db,storeName){var transaction=db.transaction(storeName);var store=transaction.objectStore(storeName);var request=store.openCursor();request.onsuccess=function(e){var cursor=e.target.result;if(cursor){console.log(cursor.key);var currentStudent=cursor.value;console.log(currentStudent.name);cursor.continue();}};}

curson.contine()会使游标下移，知道没有数据返回undefined

index与游标结合

要想获取age为26的student，可以结合游标使用索引

function getMultipleData(db,storeName){var transaction=db.transaction(storeName);var store=transaction.objectStore(storeName);var index = store.index("ageIndex");var request=index.openCursor(IDBKeyRange.only(26))request.onsuccess=function(e){var cursor=e.target.result;if(cursor){var student=cursor.value;console.log(student.id);cursor.continue();}}}

这样我们可是使用索引打开一个游标，参数下面会讲到，在成功的句柄内获得游标便利age为26的student，也可以通过index.openKeyCursor()方法只获取每个对象的key值。

指定游标范围

index.openCursor()/index.openKeyCursor()方法在不传递参数的时候会获取object store所有记录，像上面例子一样我们可以对搜索进行筛选

可以使用key range 限制游标中值的范围，把它作为第一个参数传给 openCursor() 或是 openKeyCursor()

IDBKeyRange.only(value):只获取指定数据

IDBKeyRange.lowerBound(value,isOpen)：获取最小是value的数据，第二个参数用来指示是否排除value值本身，也就是数学中的是否是开区间

IDBKeyRange.upperBound(value,isOpen)：和上面类似，用于获取最大值是value的数据

IDBKeyRange.bound(value1,value2,isOpen1,isOpen2)：不用解释了吧

获取名字首字母在B-E的student

function getMultipleData(db,storeName){var transaction=db.transaction(storeName);var store=transaction.objectStore(storeName);var index = store.index("nameIndex");var request=index.openCursor(IDBKeyRange.bound('B','F',false,

true

));request.onsuccess=function(e){var cursor=e.target.result;if(cursor){var student=cursor.value;console.log(student.name);cursor.continue();}}}

完整示例

  1 <!DOCTYPE HTML>
  2 <html>
  3 <head>
  4     <title>IndexedDB</title>
  5 </head>
  6 <body>
  7     <script type="text/javascript">
  8         function openDB (name,version) {
  9             var version=version || 1;
 10             var request=window.indexedDB.open(name,version);
 11             request.onerror=function(e){
 12                 console.log(e.currentTarget.error.message);
 13             };
 14             request.onsuccess=function(e){
 15                 myDB.db=e.target.result;
 16             };
 17             request.onupgradeneeded=function(e){
 18                 var db=e.target.result;
 19                 if(!db.objectStoreNames.contains('students')){
 20                     var store=db.createObjectStore('students',{keyPath: 'id'});
 21                     store.createIndex('nameIndex','name',{unique:true}); 
 22                     store.createIndex('ageIndex','age',{unique:false}); 
 23                 }
 24                 console.log('DB version changed to '+version);
 25             };
 26         }
 27 
 28         function closeDB(db){
 29             db.close();
 30         }
 31 
 32         function deleteDB(name){
 33             indexedDB.deleteDatabase(name);
 34         }
 35 
 36         function addData(db,storeName){
 37             var transaction=db.transaction(storeName,'readwrite'); 
 38             var store=transaction.objectStore(storeName); 
 39 
 40             for(var i=0;i<students.length;i++){
 41                 store.add(students[i]);
 42             }
 43         }
 44 
 45         function getDataByKey(db,storeName,value){
 46             var transaction=db.transaction(storeName,'readwrite'); 
 47             var store=transaction.objectStore(storeName); 
 48             var request=store.get(value); 
 49             request.onsuccess=function(e){ 
 50                 var student=e.target.result; 
 51                 console.log(student.name); 
 52             };
 53         }
 54 
 55         function updateDataByKey(db,storeName,value){
 56             var transaction=db.transaction(storeName,'readwrite'); 
 57             var store=transaction.objectStore(storeName); 
 58             var request=store.get(value); 
 59             request.onsuccess=function(e){ 
 60                 var student=e.target.result; 
 61                 student.age=35;
 62                 store.put(student); 
 63             };
 64         }
 65 
 66         function deleteDataByKey(db,storeName,value){
 67             var transaction=db.transaction(storeName,'readwrite'); 
 68             var store=transaction.objectStore(storeName); 
 69             store.delete(value); 
 70         }
 71 
 72         function clearObjectStore(db,storeName){
 73             var transaction=db.transaction(storeName,'readwrite'); 
 74             var store=transaction.objectStore(storeName); 
 75             store.clear();
 76         }
 77 
 78         function deleteObjectStore(db,storeName){
 79             var transaction=db.transaction(storeName,'versionchange'); 
 80             db.deleteObjectStore(storeName);
 81         }
 82 
 83         function fetchStoreByCursor(db,storeName){
 84             var transaction=db.transaction(storeName);
 85             var store=transaction.objectStore(storeName);
 86             var request=store.openCursor();
 87             request.onsuccess=function(e){
 88                 var cursor=e.target.result;
 89                 if(cursor){
 90                     console.log(cursor.key);
 91                     var currentStudent=cursor.value;
 92                     console.log(currentStudent.name);
 93                     cursor.continue();
 94                 }
 95             };
 96         }
 97 
 98         function getDataByIndex(db,storeName){
 99             var transaction=db.transaction(storeName);
100             var store=transaction.objectStore(storeName);
101             var index = store.index("ageIndex");
102             index.get(26).onsuccess=function(e){
103                 var student=e.target.result;
104                 console.log(student.id);
105             }
106         }
107 
108         function getMultipleData(db,storeName){
109             var transaction=db.transaction(storeName);
110             var store=transaction.objectStore(storeName);
111             var index = store.index("nameIndex");
112             var request=index.openCursor(null,IDBCursor.prev);
113             request.onsuccess=function(e){
114                 var cursor=e.target.result;
115                 if(cursor){
116                     var student=cursor.value;
117                     console.log(student.name);
118                     cursor.continue();
119                 }
120             }
121         }
122 
123         var myDB={
124             name:'test',
125             version:1,
126             db:null
127         };
128 
129         var students=[{ 
130             id:1001, 
131             name:"Byron", 
132             age:24 
133         },{ 
134             id:1002, 
135             name:"Frank", 
136             age:30 
137         },{ 
138             id:1003, 
139             name:"Aaron", 
140             age:26 
141         },{ 
142             id:1004, 
143             name:"Casper", 
144             age:26 
145         }]; 
146     </script>
147 </body>
148 </html>