HTML5本地存储——IndexedDB（二：索引）

十度 HTML5 2016年04月29日收藏

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

 <!DOCTYPE HTML>
<html>
<head>
    <title>IndexedDB</title>
</head>
<body>
    <script type="text/javascript">
        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);
            };
        }

        function closeDB(db){
            db.close();
        }

        function deleteDB(name){
            indexedDB.deleteDatabase(name);
        }

        function addData(db,storeName){
            var transaction=db.transaction(storeName,'readwrite'); 
            var store=transaction.objectStore(storeName); 

            for(var i=0;i<students.length;i++){
                store.add(students[i]);
            }
        }

        function getDataByKey(db,storeName,value){
            var transaction=db.transaction(storeName,'readwrite'); 
            var store=transaction.objectStore(storeName); 
            var request=store.get(value); 
            request.onsuccess=function(e){ 
                var student=e.target.result; 
                console.log(student.name); 
            };
        }

        function updateDataByKey(db,storeName,value){
            var transaction=db.transaction(storeName,'readwrite'); 
            var store=transaction.objectStore(storeName); 
            var request=store.get(value); 
            request.onsuccess=function(e){ 
                var student=e.target.result; 
                student.age=35;
                store.put(student); 
            };
        }

        function deleteDataByKey(db,storeName,value){
            var transaction=db.transaction(storeName,'readwrite'); 
            var store=transaction.objectStore(storeName); 
            store.delete(value); 
        }

        function clearObjectStore(db,storeName){
            var transaction=db.transaction(storeName,'readwrite'); 
            var store=transaction.objectStore(storeName); 
            store.clear();
        }

        function deleteObjectStore(db,storeName){
            var transaction=db.transaction(storeName,'versionchange'); 
            db.deleteObjectStore(storeName);
        }

        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();
                }
            };
        }

        function getDataByIndex(db,storeName){
            var transaction=db.transaction(storeName);
            var store=transaction.objectStore(storeName);
            var index = store.index("ageIndex");
            index.get(26).onsuccess=function(e){
                var student=e.target.result;
                console.log(student.id);
            }
        }

        function getMultipleData(db,storeName){
            var transaction=db.transaction(storeName);
            var store=transaction.objectStore(storeName);
            var index = store.index("nameIndex");
            var request=index.openCursor(null,IDBCursor.prev);
            request.onsuccess=function(e){
                var cursor=e.target.result;
                if(cursor){
                    var student=cursor.value;
                    console.log(student.name);
                    cursor.continue();
                }
            }
        }

        var myDB={
            name:'test',
            version:1,
            db:null
        };

        var students=[{ 
            id:1001, 
            name:"Byron", 
            age:24 
        },{ 
            id:1002, 
            name:"Frank", 
            age:30 
        },{ 
            id:1003, 
            name:"Aaron", 
            age:26 
        },{ 
            id:1004, 
            name:"Casper", 
            age:26 
        }]; 
    </script>
</body>
</html>

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