Using LINQ to Indexed DB

While the library is still under development, I want to take some time to explain how you can use this framework, and show how easy it gets to work with the Indexed DB. As mentioned before, the library is based on the on the Promises context. This way we can easily handle all the async callbacks on which the Indexed DB API is based, and provide a uniform object to the developer for handling the results and/or errors. And by using the progress callback, we can provide returning multiple records one by one instead of a whole collection in the complete callback. For more information about promises:

• jQuery promise
• WinJS promise

Another strength of the library is, that you get the opportunity to let it auto build it’s structure. It’s not necessary to provide the database structure. You can just start writing queries, and the library will take care of the creation of tables and indexes. This way it can easily be used for writing POCs or demo applications. This means when ever you are mentioning a string value in the from method that isn’t known in the object store collection, it will be created for you.

But enough about the theory, let us watch some code.

Setting UP Linq2indexeddb

The first thing you need to do is getting the linq2indexeddb library. You can do this by getting the JS script files from codeplex. The only thing you need to make sure is: the sort.js and where.js file need to be in a “Script” folder under the root of the project. These files are used to preform web worker tasks and are hardcoded referenced for now.

Or VS developers can use Nuget Packages:

• http://www.myget.org/feed/Packages/linq2indexeddb (jQuery version)
• http://www.myget.org/feed/Packages/linq2indexeddbmetro (Win8 version, using WinJS)

Once you have the linq2indexeddb library, the next thing you need to do is adding a reference to it in your page. Note, if you are using the jQuery version, you need to add a reference to the jQuery framework first.

using Linq2indexeddb

Once all the references are added, we can start using the library. The first thing you need to do is creating a instance of the linq2indexeddb object. You can do this by calling the linq2indexeddb method on the window object. This method accepts 3 parameters:

• The first one is the name of the database u want to use.
• The second one is a database configuration object. More on that later on the post.
• The last is an Boolean which allows you to enable logging. By default this is disabled

   1: var db = window.linq2indexedDB("dbName", dbConfig, false);

Configuring the database

When opening/creating the database, you can provide a database configuration. Here you can configure the object stores and indexes you want to use. There are several ways to do the configuration, but one thing needs to be provided at all time: the version of the database. This makes sure that the database will have the correct structure we need.

   1: var dbConfig = {};

   2: dbConfig.version = 1;

A second thing we need to do, is providing a way to define the structure. In the current implementation of the library, there are 4 ways to do this. For now I would advise you to use the definition. This doesn’t require you to write the create/delete statements your self. But if you do want to, you can make use of the promises present in the linq2indexeddb.core to create/delete object stores and indexes.

onupgradeneeded

This a function that gets called when the database needs to get updated to the most recent version you provided in the configuration object. 3 parameters are passed to this function:

• Transaction: on this transaction you can create/delete object stores and indexes
  
• The current version of the database
  
• The version the database is upgrading to.

   1: dbConfig.onupgradeneeded = 

   2:     function (transaction, oldVersion, newVersion){

   3:         // Code to upgrade the db structure

   4:     }

The onupgradeneeded callback is the only one that can’t be used in combination with one of the other ways to define the function

schema

The schema is an object which defines the several versions as a key/value. The key keeps the version it targets and in the value an upgrade function. In this function you can add your code to upgrade the database to the version given in the key. The upgrade function has one parameter:

• Transaction: on this transaction you can create/delete object stores and indexes

   1: dbConfig.schema = {

   2:     1: function (transaction){

   3:             // Code to upgrade the db structure to version 1

   4:        }

   5:     2: function (transaction){

   6:             // Code to upgrade the db structure to version 2

   7:        }

   8: }

Note: If the database needs to upgrade from version 0 to 2, the upgrade function of version 1 gets called first. When the upgrade to version 1 is done, the upgrade function of version 2 gets called.

definition

The definition object is the only way to define your database structure without having to write upgrade code. The object keeps a collection of objects which describe what needs to be added or removed for a version. Each object exists out of the following properties:

• Version: The version where for the definitions are.
  
• objectStores: Collection of objects that define an object store
  
  
  
  • name: the name of the object store
    
  • objectStoreOptions
    
    
    
    • autoincrement: defines if the key is handled by the database
      
    • keyPath: the name of the property that keeps the key for the object store
    
    
  • remove: indicates if the object store must be removed
  
  
• indexes: Collection of objects that define an index
  
  
  
  • objectStoreName: the name of the object store where the index needs to be created on
    
  • propertyName: the name of the property where for we want to add an index
    
  • indexOptions
    
    
    
    • unique: defines if the value of this property needs to be unique
      
    • multirow: Defines the way keys are handled that have an array value in the key
    
    
  • remove: indicates if the index must be removed
  
  
• defaultData: Collection of default data that needs to be added in the version
  
  
  
  • objectStoreName: the name of the object store where we want to add the data
    
  • data: the data we want to add
    
  • key: the key of the data
    
  • remove: indicates if the data needs to be removed

   1: dbConfig.definition= [{

   2:     version: 1,

   3:     objectStores: [{ name: "ObjectStoreName"

   4:                        , objectStoreOptions: { autoIncrement: false

   5:                                              , keyPath: "Id" } 

   6:                    }]

   7:     indexes: [{ objectStoreName: "ObjectStoreName"

   8:                   , propertyName: "PropertyName"

   9:                   , indexOptions: { unique: false, multirow: false } 

  10:               }],

  11:     defaultData: [{ objectStoreName: ObjectStoreName

  12:                       , data: { Id: 1, Description: "Description1" }

  13:                       , remove: false },

  14:                   { objectStoreName: ObjectStoreName

  15:                       , data: { Id: 2, Description: "Description2" }

  16:                       , remove: false },

  17:                   { objectStoreName: ObjectStoreName

  18:                         , data: { Id: 3, Description: "Description3" }

  19:                         , remove: false }]

  20: }];

onversionchange

This a function that gets called when the database needs to get updated to the most recent version you provided in the configuration object. But in contrast to the onupgradeneeded callback, this function can be called multiple times. For example if an database is upgrading from version 0 to version 2, the onversionchange will be called 2 times. Once for version 1 and once for version 2.  2 parameters are passed to the function:

• Transaction: on this transaction you can create/delete object stores and indexes
  
• The version of the database it is upgrading to.

   1: dbConfig.onversionchange = 

   2:     function (transaction, version){

   3:         // Code to upgrade the db structure

   4:     }

Querying data

Once the database structure is created, we can start querying on it. On the linq2indexeddb object we have a field linq which holds all the linq functionality. The first method you always need to call is the from method. This method excepts only one parameter, the name of the object store we want to work on. Once we have this we can start inserting, updating, deleting and selecting data from it.

   1: // inserting data, key is optional

   2: db.linq.from("objectstore").insert({}, key);

   3: // updating data, key is optional

   4: db.linq.from("objectstore").update({}, key);

   5: // removing data

   6: db.linq.from("objectstore").remove(id);

   7: // clears all data from the object store

   8: db.linq.from("objectstore").clear();

   9: // gets a single record by his key

  10: db.linq.from("objectstore").get(key);

  11: // selects all objects

  12: db.linq.from("objectstore").select();

But the library also provides ways to filter data. This can be done by calling the where method. This accepts the name of the property we want to filter on as parameter. On this you can call the filter you want to add. For now these are limited to the following:

• equals(value)
  
• between(value1, value2, value1included, value2included)
  
• greaterThen(value, valueIncluded)
  
• smallerThen(value, valueIncluded)
  
• inArray(arrayOfObjects)
  
• like(value)

So if we want to select all the objects which have a field called '”property” and have the value “value” we write the following query:

   1: db.linq.from("objectstore").where("property").equals("value").select()

If you want to add multiple filters you need to do the following:

   1: db.linq.from("objectstore")

   2:        .where("property").equals("value")

   3:        .and("anotherproperty").greaterThen(4)

   4:        .select()

You are also able to sort your data:

• orderBy(propertyName)


• orderByDesc(propertyName)

   1: db.linq.orderBy("property").select()

As last, the library also enables you to get only a subset of the properties stored in the objects

   1: db.linq.from("objectstore").select(["property1", "property2"])

Conclusion

This was a brief introduction of the functionalities of the linq2indexeddb library. In future post I will go more in-depth into the advanced functionalities like linq2indexeddb.core. If you have any suggestions, bugs, additions,… about the library, feel free to contact me. Hope you enjoy using the library.