Getting Started with HTML5 INDEXEDDB database (ii)

The previous study notes on Indexeddb mainly wrote the basic operation of INDEXEDDB database-adding and deleting; but why should we use INDEXEDDB? Why has indexeddb been favored by developers? The main thing is the core features of INDEXEDDB: With cursors and indexes and scopes to really play INDEXEDDB power

1. Index: Why is it called INDEXEDDB? Because it gives us the index to query the value we need;

2. Cursors: Cursors provide us with the data that we iterate over,

3, the scope: and the cursor together specify the range we need to loop,

4, index, cursor, scope of comprehensive application can bring us a good data interaction experience

To create an index:

1request.onupgradeneeded =function(event) {2db =Event.target.result;3     if(!db.objectstorenames.contains ("table")) {4         varstore = Db.createobjectstore ("table", {keypath: "ssn"});5     }6     varindex = Store.createindex ("Nameindex", "name", {unique:true});//create name index, follow we can find by name7Console.log ("Createobjectstore success!");8};

To read data through a cursor:

1Db.transaction ("table"). ObjectStore ("table"). OpenCursor (). onsuccess =function(Event) {//opencursor method2     vargetString = "";3     varcursor =Event.target.result;4     if(cursor) {5GetString + = "Name for SSN" + Cursor.key + "is" +Cursor.value.name;6Console.log ("Name for SSN" + Cursor.key + "is" +cursor.value.name);7Cursor.Continue();8         //alert (getString);9     }Tendocument.getElementById ("Get_ssn"). InnerHTML + = getstring+ "<br/>"; One}

Find/Read data by index://If an index is created when the data table is created or not accessed through the index

1 db.transaction ("table")2 . ObjectStore ("table")3 . Index ("Nameindex" )4 . Get ("Chenjian")5function() {6     Console.log (this. result.email); 7 };

Mixed application of index and cursors cursor:

1Db.transaction ("Table")2. ObjectStore ("table")3. Index ("Nameindex")4 . OpenCursor (Idbkeyrange.only ("Chenjian"))5. onsuccess =function() {6     varcursor =Event.target.result;7     if(cursor) {8Console.log (Cursor.key +cursor.value.name);9Cursor.Continue();Ten     } One};

The OpenCursor () method can pass in the specified range of parameters:

Specify the range:

1 index.opencursor () the/index.openkeycursor () method takes all the records of the object store when the parameter is not passed, as in the example above we can filter the search 2 You can use the key range to limit the range of values in a cursor, passing it as the first argument to OpenCursor () or openkeycursor () 3 idbkeyrange.only (value): Gets only the specified data 4 Idbkeyrange.lowerbound (Value,isopen): Gets the data with the smallest value, and the second parameter indicates whether to exclude the value itself, that is, whether it is an open interval in mathematics 5 Idbkeyrange.upperbound (Value,isopen): Similar to the above, the data used to get the maximum value is value 6 Idbkeyrange.bound (VALUE1,VALUE2,ISOPEN1,ISOPEN2): no need to explain.

When a specified range is passed in, the cursor will only loop through the range

Getting Started with HTML5 INDEXEDDB database (ii)