IndexedDB学习二：使用

目标

• 打开数据库连接，开始一个事物
• 创建存储对象
• 请求数据库操作：比如添加或查询数据。
• 等待操作完成， 监听正确的DOM事件。
• 对结果进行其它操作。

创建和构建数据存储

使用一个稳定版本的IndexedDB

// In the following line, you should include the prefixes of implementations you want to test.
window.indexedDB = window.indexedDB || window.mozIndexedDB || window.webkitIndexedDB || window.msIndexedDB;
// DON'T use "var indexedDB = ..." if you're not in a function.
// Moreover, you may need references to some window.IDB* objects:
window.IDBTransaction = window.IDBTransaction || window.webkitIDBTransaction || window.msIDBTransaction;
window.IDBKeyRange = window.IDBKeyRange || window.webkitIDBKeyRange || window.msIDBKeyRange
// (Mozilla has never prefixed these objects, so we don't need window.mozIDB*)
if (!window.indexedDB) {
    window.alert("Your browser doesn't support a stable version of IndexedDB. Such and such feature will not be available.")
}

打开数据库

// Let us open our database
var request = window.indexedDB.open("MyTestDatabase");
// open a database with version number
var request = indexedDB.open("MyTestDatabase", 3);

处理机制

var db;
var request = indexedDB.open("MyTestDatabase");
request.onerror = function(event) {
  // Do something with request.errorCode!
};
request.onsuccess = function(event) {
  // Do something with request.result!
  db = request.result;
};

处理错误

db.onerror = function(event) {
  // Generic error handler for all errors targeted at this database's
  // requests!
  alert("Database error: " + event.target.errorCode);
};

创建和更新数据库版本

// This event is only implemented in recent browsers
request.onupgradeneeded = function(event) { 
   // Update object stores and indices .... 
};

构建数据库

IndexedDB 使用对象存储空间而不是表，并且一个单独的数据库可以包含任意数量的对象存储空间。每当一个值被存储进一个对象存储空间时，它会被和一个键相关联。键的提供可以有几种不同的方法，这取决于对象存储空间是使用 key path 还是 key generator。

事务可以接收三种不同类型的 DOM 事件： error，abort，以及 complete。如果在 error 事件上通过调用 preventDefault() 处理了这个错误，整个事务被回滚了。如果在事务中调用 abort()，那么事务被回滚并且有关事物的一个 abort 事件被触发。

// This is what our customer data looks like.
const customerData = [
  { ssn: "444-44-4444", name: "Bill", age: 35, email: "[e-mail]" },
  { ssn: "555-55-5555", name: "Donna", age: 32, email: "[e-mail]" }
];
const dbName = "the_name";

var request = indexedDB.open(dbName, 2);
 
request.onerror = function(event) {
  // Handle errors.
};
request.onupgradeneeded = function(event) {
  var db = event.target.result;
 
  // Create an objectStore to hold information about our customers. We're
  // going to use "ssn" as our key path because it's guaranteed to be
  // unique.
  var objectStore = db.createObjectStore("customers", { keyPath: "ssn" });
 
  // Create an index to search customers by name. We may have duplicates
  // so we can't use a unique index.
  objectStore.createIndex("name", "name", { unique: false });
 
  // Create an index to search customers by email. We want to ensure that
  // no two customers have the same email, so use a unique index.
  objectStore.createIndex("email", "email", { unique: true });
 
  // Store values in the newly created objectStore.
  for (var i in customerData) {
    objectStore.add(customerData[i]);
  }
};

onupgradeneeded是修改数据结构的唯一方法。
createObjectStore是创建数据对象的方法。例子中可以通过SSN获取存储对象。

添加和删除数据

// adding data
var transaction = db.transaction(["customers"], "readwrite");
transaction.oncomplete = function(event) {
  alert("All done!");
};
 
transaction.onerror = function(event) {
  // Don't forget to handle errors!
};
 
var objectStore = transaction.objectStore("customers");
for (var i in customerData) {
  var request = objectStore.add(customerData[i]);
  request.onsuccess = function(event) {
    // event.target.result == customerData[i].ssn
  };
}
// removing data
var request = db.transaction(["customers"], "readwrite")
                .objectStore("customers")
                .delete("444-44-4444");
request.onsuccess = function(event) {
  // It's gone!
};

查询数据

var transaction = db.transaction(["customers"]);
var objectStore = transaction.objectStore("customers");
var request = objectStore.get("444-44-4444");
request.onerror = function(event) {
  // Handle errors!
};
request.onsuccess = function(event) {
  // Do something with the request.result!
  alert("Name for SSN 444-44-4444 is " + request.result.name);
};

使用游标

var objectStore = db.transaction("customers").objectStore("customers");
 
objectStore.openCursor().onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    alert("Name for SSN " + cursor.key + " is " + cursor.value.name);
    cursor.continue();
  }
  else {
    alert("No more entries!");
  }
};
// or retriving data and put into the object
var customers = [];
 
objectStore.openCursor().onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    customers.push(cursor.value);
    cursor.continue();
  }
  else {
    alert("Got all customers: " + customers);
  }
};

使用索引

var index = objectStore.index("name");
index.get("Donna").onsuccess = function(event) {
  alert("Donna's SSN is " + event.target.result.ssn);
};
// or more complicated...
index.openCursor().onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // cursor.key is a name, like "Bill", and cursor.value is the whole object.
    alert("Name: " + cursor.key + ", SSN: " + cursor.value.ssn + ", email: " + cursor.value.email);
    cursor.continue();
  }
};
 
index.openKeyCursor().onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // cursor.key is a name, like "Bill", and cursor.value is the SSN.
    // No way to directly get the rest of the stored object.
    alert("Name: " + cursor.key + ", SSN: " + cursor.value);
    cursor.continue();
  }
};

设定游标范围和移动方向

// Only match "Donna"
var singleKeyRange = IDBKeyRange.only("Donna");
 
// Match anything past "Bill", including "Bill"
var lowerBoundKeyRange = IDBKeyRange.lowerBound("Bill");
 
// Match anything past "Bill", but don't include "Bill"
var lowerBoundOpenKeyRange = IDBKeyRange.lowerBound("Bill", true);
 
// Match anything up to, but not including, "Donna"
var upperBoundOpenKeyRange = IDBKeyRange.upperBound("Donna", true);
 
//Match anything between "Bill" and "Donna", but not including "Donna"
var boundKeyRange = IDBKeyRange.bound("Bill", "Donna", false, true);
 
index.openCursor(boundKeyRange).onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // Do something with the matches.
    cursor.continue();
  }
};
// descending...
objectStore.openCursor(null, IDBCursor.prev).onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // Do something with the entries.
    cursor.continue();
  }
};
// in the following, IDBCursor.nextunique can also be IDBCursor.prevunique
index.openKeyCursor(null, IDBCursor.nextunique).onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // Do something with the entries.
    cursor.continue();
  }
};

当WEB应用在另一个TAB中打开时更改版本

var openReq = mozIndexedDB.open("MyTestDatabase", 2);
 
openReq.onblocked = function(event) {
  // If some other tab is loaded with the database, then it needs to be closed
  // before we can proceed.
  alert("Please close all other tabs with this site open!");
};
   
openReq.onupgradeneeded = function(event) {
  // All other databases have been closed. Set everything up.
  db.createObjectStore(/* ... */);
  useDatabase(db);
}  
   
openReq.onsuccess = function(event) {
  var db = event.target.result;
  useDatabase(db);
  return;
}
 
function useDatabase(db) {
  // Make sure to add a handler to be notified if another page requests a version
  // change. We must close the database. This allows the other page to upgrade the database.
  // If you don't do this then the upgrade won't happen until the user close the tab.
  db.onversionchange = function(event) {
    db.close();
    alert("A new version of this page is ready. Please reload!");
  };
 
  // Do stuff with the database.

安全

完整的实例
https://developer.mozilla.org/en-US/docs/IndexedDB/Using_IndexedDB