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  • What do you name the "other" kind of view-model in an MVVM project?

    - by DanM
    With MVVM, I think of a view-model as a class that provides all the data and commands that a view needs to bind to. But what happens when I have a database entity object, say a Customer, and I want to build a class that shapes or flattens the Customer class for use in a data grid. For example, maybe this special Customer object would have a property TotalOrders, which is actually calculated using a join with a collection of Order entities. My question is, what do I call this special Customer class? In other situations, I'd be tempted to call it a CustomerViewModel, but I feel like "overloading" the notion of a view-model like this would be confusing in an MVVM project. What would you suggest?

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  • Application logic for invoicing and subscriptions?

    - by Industrial
    Hi everyone, We're just in the planning stage of a web app that offers subscriptions to our customers. The subscription periods varies and can be prolonged indefinitely by our customers, but are always at least one month (30 days). When a customer signs up, the customer information (billing address, phone number and so on) are stored in a customers table and a subscription is created in the subscriptions table: id | start_date | end_date | customer_id -------------------------------------------------------- 1 | 2010-12-31 | 2011-01-31 | 1 Every month we'll loop through the subscriptions table (cronjob preferably) and create invoices for the past subscription period, which are housed in their own table - invoices. Depending on the customer, invoices are manually printed out and sent by mail, or just emailed to the customer. Due to the nature of our customers and the product, we need to offer a variety of different payment alternatives including wire transfer and card payments, hence some invoices may need to be manually handled and registered as paid by our staff. The 15th every month, the invoices table are looped through and if no payment has been marked for the actual invoice, the according subscription will be removed. If there's a payment registered, the end_date in the subscriptions table is incremented by another 30 days (or what now our period our customer has chosen). Are we looking at headaches by incrementing dates forwards and backwards to handle non-paying customers and extending subscriptions? Would it be a better idea to add new subscriptions as customers extends their subscription?

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  • Detemining a database's OS with a SQL query?

    - by KaizenSoze
    I'm writing a tool to gather customer configuration information. One of the questions I want to answer, what OS is the customer database running on. I haven't found a generic way to find the OS with SQL and I can't create stored procedures on the customer's database. If there is a way, it's probably vendor specific. Suggestions? Thanks in advance.

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  • Hibernate mapping to manage bidirectional relationship using intermediate table

    - by shikarishambu
    I have an object hierarchy that is as follows. Party inherited by Organization and Person Organization inherited by Customer, Vendor Person inherited by Contact In the database I have the following tables Party, Customer, Vendor, Contact. All of them have a corresponding row in Party table. Contact belongs to either Vendor or Customer. I have a field on the Contact table for org_party_id. However, since the organization can be either a Customer or Vendor I need to be able to look at different tables. Is there a way to map this in hibernate? Or, a better way to manage it in DB/ hibernate?

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  • easy mysql query question

    - by Ahmet vardar
    Hi, here is the "msg" table on mysql sent_to customer msg read ------- -------- ------ ----- 45 3 bla 0 34 4 bla 1 34 6 bla 0 45 3 bla 0 56 7 bla 1 45 8 bla 0 for example user whose id number is 45 logs in, i want him to see this, you have 2 unread msg to your "number 3" customer you have 1 unread msg to your "number 8" customer like a news feed what query should i use for this ? thx

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  • CakePHP - recursive on specific fields in model?

    - by Paul
    Hi, I'm pretty new to CakePHP but I think I'm starting to get the hang of it. I'm trying to pull related table information recursively, but I want to specify which related models to recurse on. Let me give you an example to demonstrate my goal: I have a model "Customer", which has info like Company name, website, etc. "Customer" hasMany "Addresses", which contain info for individual contacts like Contact Name, Street, City, State, Country, etc. "Customer" also belongsTo "CustomerType", which is just has descriptive category info - a name and description, like "Distributor" or "Manufacturer". When I do a find on "Customer" I want to get associated "CustomerType" and "Address" info as sub-arrays, and this works fine just by setting up the hasMany and belongsTo associations properly. But now, here's my issue: I want to get associated State/Country info. So, instead of each "Address" array row just having "state_id", I want it to have "state" = array("id" = 20, "name" = "New York",...) etc. If I set $recursive to a higher value (e.g., 2) in the Partner model, I get what I want for the State/Country info in each "Address". BUT it also recurses on "CustomerType", and that results in the "CustomerType" field of my "Partner" object having a huge array of all Customer objects that match that type, which could be thousands long. So the point is, I DON'T want to recurse on "CustomerType", only on "Address". Is there a way I can set this up? Sorry for the long-winded question, and thanks in advance!

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  • How can I [simply] consume JSON Data in a Line of Business Web Application

    - by Atomiton
    I usually use JSON with jQuery to just return a string with html. However, I want to start to use Javascript objects in my code. What's the simplest way to get started using json objects on my page? Here's a sample Ajax call ( after $(document).ready( { ... }) of course: $('#btn').click(function(event) { event.preventDefault(); var out = $('#result'); $.ajax({ url: "CustomerServices.asmx/GetCustomersByInvoiceCount", success: function(msg) { // // Iterate through the json results and spit them out to a page? // }, data: "{ 'invoiceCount' : 100 }" }); }); My WebMethod: [WebMethod(Description="Gets customers with more than n invoices")] public List<Customer> GetCustomersByInvoiceCount(int? invoiceCount) { using (dbDataContext db = new dbDataContext()) { return db.Customers.Where(c => c.InvoiceCount >= invoiceCount); } } What gets returned: {"d":[{"__type":"Customer","Account":"1116317","Name":"SOME COMPANY","Address":"UNit 1 , 392 JOHN ST. ","LastTransaction":"\/Date(1268294400000)\/","HighestBalance":13922.34},{"__type":"Customer","Account":"1116318","Name":"ANOTHER COMPANY","Address":"UNIT #345 , 392 JOHN ST. ","LastTransaction":"\/Date(1265097600000)\/","HighestBalance":549.42}]} What I'd LIKE to know, is what are people generally doing with this returned json? Do you iterate through the properties and create an html table on the fly? Is there way to "bind" JSON data using a javascript version of reflection ( something like the .Net GridView Control ) Do you throw this returned data into a Javascript Object and then do something with it? An example of what I want to achieve is to have an plain ol' html page ( on a mobile device )with a list of a Salesperson's Customers. When one of those customers are clicked, the customer id gets sent to a webservice which retrieves the customer details that are relevant to a sales person. I know the SO talent pool is quite deep so I figured you all here would be able to guide in the right direction and give me a few ideas on the best way to approach this.

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  • List remove question

    - by younevertell
    List collCustList = new List(); collCustList.Add(new Customer(99, "H", "P")); I tried collCustList.Remove(new Customer(99, "H", "P")); but it doesn't work How could I remove the new item(new Customer(99, "H", "P")) I just added? Thanks

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  • Joining tables with composite keys in a legacy system in hibernate

    - by Steve N
    Hi, I'm currently trying to create a pair of Hibernate annotated classes to load (read only) from a pair of tables in a legacy system. The legacy system uses a consistent (if somewhat dated) approach to keying tables. The tables I'm attempting to map are as follows: Customer CustomerAddress -------------------------- ---------------------------- customerNumber:string (pk) customerNumber:string (pk_1) name:string sequenceNumber:int (pk_2) street:string postalCode:string I've approached this by creating a CustomerAddress class like this: @Entity @Table(name="CustomerAddress") @IdClass(CustomerAddressKey.class) public class CustomerAddress { @Id @AttributeOverrides({ @AttributeOverride(name = "customerNumber", column = @Column(name="customerNumber")), @AttributeOverride(name = "sequenceNumber", column = @Column(name="sequenceNumber")) }) private String customerNumber; private int sequenceNumber; private String name; private String postalCode; ... } Where the CustomerAddressKey class is a simple Serializable object with the two key fields. The Customer object is then defined as: @Entity @Table(name = "Customer") public class Customer { private String customerNumber; private List<CustomerAddress> addresses = new ArrayList<CustomerAddress>(); private String name; ... } So, my question is: how do I express the OneToMany relationship on the Customer table?

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  • SQL Server 2008 - Get Latest Record from Joined Table

    - by user336786
    Hello, I have a SQL Server 2008 database. This database has two tables called Customer and Order. These tables are defined as follows: Customer -------- ID, First Name, Last Name Order ----- ID, CustomerID, Date, Description I am trying to write a query that returns all of the customers in my database. If the user has placed at least one order, I want to return the information associated with the most recent order placed. Currently, I have the following: SELECT * FROM Customer c LEFT OUTER JOIN Order o ON c.[ID]=o.[CustomerID] As you can imagine, this will return all of the orders associated with a customer. In reality though, I only want the most recent one. How do I do this in SQL? Thank you!

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  • Overriding inherited generic methods

    - by jess
    I have this code in base class protected virtual bool HasAnyStuff<TObject>(TObject obj) where TObject:class { return false; } In child class I am overriding protected override bool HasAnyStuff<Customer>(Customer obj) { //some stuff if Customer.sth etc return false; } I am getting this error '''Type parameter declaration must be an identifier not a type''' What is it I am doing wrong here?

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  • How can I [simply] consume JSON Data to display to the page

    - by Atomiton
    I usually use JSON with jQuery to just return a string with html. However, I want to start to use Javascript objects in my code. What's the simplest way to get started using json objects on my page? Here's a sample Ajax call ( after $(document).ready( { ... }) of course: $('#btn').click(function(event) { event.preventDefault(); var out = $('#result'); $.ajax({ url: "CustomerServices.asmx/GetCustomersByInvoiceCount", success: function(msg) { // // Iterate through the json results and spit them out to a page? // }, data: "{ 'invoiceCount' : 100 }" }); }); My WebMethod: [WebMethod(Description="Gets customers with more than n invoices")] public List<Customer> GetCustomersByInvoiceCount(int? invoiceCount) { using (dbDataContext db = new dbDataContext()) { return db.Customers.Where(c => c.InvoiceCount >= invoiceCount); } } What gets returned: {"d":[{"__type":"Customer","Account":"1116317","Name":"SOME COMPANY","Address":"UNit 1 , 392 JOHN ST. ","LastTransaction":"\/Date(1268294400000)\/","HighestBalance":13922.34},{"__type":"Customer","Account":"1116318","Name":"ANOTHER COMPANY","Address":"UNIT #345 , 392 JOHN ST. ","LastTransaction":"\/Date(1265097600000)\/","HighestBalance":549.42}]} What I'd LIKE to know, is what are people generally doing with this returned json? Do you iterate through the properties and create an html table on the fly? Is there way to "bind" JSON data using a javascript version of reflection ( something like the .Net GridView Control ) Do you throw this returned data into a Javascript Object and then do something with it? An example of what I want to achieve is to have an plain ol' html page ( on a mobile device )with a list of a Salesperson's Customers. When one of those customers are clicked, the customer id gets sent to a webservice which retrieves the customer details that are relevant to a sales person. I know the SO talent pool is quite deep so I figured you all here would be able to guide in the right direction and give me a few ideas on the best way to approach this.

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  • JQuery + Rails + Select Menu

    - by blackpond
    I want to have a select menu to change a field on a Customer dynamically, I've never used Jquery with a select menu, and I'm having problems. The code: <% form_for @customer , :url = { :action = "update" }, :html ={:class = "ajax_form"} do |f| % Pricing: <%= select :customer, :pricing, Customer::PRICING, {}, :onchange = "$('this').closest('form').submit();" % Application.js: $(document).ready(function(){ $(".ajax_link").live("click",function(event){ //take div class = ajax_link and call this funciton when clicked. event.preventDefault(); // cancels http request $.post($(this).attr("href"), null, null, "script"); return false; }); ajaxFormSubmitHooks(); }); function ajaxFormSubmitHooks(){ $(".ajax_form").submit(function(event){ event.preventDefault(); // cancels http request $.post($(this).attr("action"), $(this).serializeArray(), null, "script"); return false; }); }

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  • need help while working on a website

    - by EqEdi
    I'm working for a website where i need to sum functionality related to sales I'm very new to the website stuff and found many things on net but don't knew what to follow. Can anybody suggest me some good tutorials which i can follow to create my website The things which i am going to work on as: saving customer information to data base using saved customer information, placing order generating bills and invoices and downloading it in pdf file format sending mails to customer with those invoice as attachments

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  • Parsing complicated query parameters

    - by Will
    My Python server receives jobs that contain a list of the items to act against, rather like a search query term; an example input: (Customer:24 OR Customer:24 OR (Group:NW NOT Customer:26)) To complicate matters, customers can join and leave groups at any time, and the job should be updated live when this happens. How is best to parse, apply and store (in my RDBMS) this kind of list of constraints?

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  • One database or many?

    - by dsims
    I am developing a website that will manage data for multiple entities. No data is shared between entities, but they may be owned by the same customer. A customer may want to manage all their entities from a single "dashboard". So should I have one database for everything, or keep the data seperated into individual databases? Is there a best-practice? What are the positives/negatives for having a: database for the entire site (entity has a "customerID", data has "entityID") database for each customer (data has "entityID") database for each entity (relation of database to customer is outside of database) Multiple databases seems like it would have better performance (fewer rows and joins) but may eventually become a maintenance nightmare.

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  • Problem with generics

    - by jess
    I have this code in base class protected virtual bool HasAnyStuff<TObject>(TObject obj) where TObject:class { return false; } In child class I am overriding protected override bool HasAnyStuff<Customer>(Customer obj) { //some stuff if Customer.sth etc return false; } I am getting this error '''Type parameter declaration must be an identifier not a type''' What is it I am doing wrong here?

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  • Performance problem on a query.

    - by yapiskan
    Hi, I have a performance problem on a query. First table is a Customer table which has millions records in it. Customer table has a column of email address and some other information about customer. Second table is a CommunicationInfo table which contains just Email addresses. And What I want in here is; how many times the email address in CommunicationInfo table repeats in Customers table. What could be the the most performer query. The basic query that I can explain this situation is; Select ci.Email, count(*) from Customer c left join CommunicationInfo ci on c.Email1 = ci.Email or c.Email2 = ci.Email Group by ci.Email But sure, it takes about 5, 6 minutes in execution. Thanks in Advance.

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  • django: how to use many-to-many relationships in values()?

    - by john
    i need to group results by a field that requires a few joins from the original model: // response_filter_args is created dynamically responses = Response.objects.filter(**response_filter_args) \ .values('customer__tags__tag') \ # django doesn't like this .annotate(average_score=Avg('rating__score')) Response - customer - tags (many-to-many field pointing to Tag) - tag (the tag as a string) Models are: class Response(models.Model): customer = models.ForeignKey(Customer) ... class Customer(models.Model): tags = models.ManyToManyField(Tag) ... class Tag(models.Model): tag = models.CharField(max_length=255) ... i'm trying to calculate average ratings. to make it work i need to tell django to group by 'tag', but it refuses to. it gives an error: Invalid field name: 'customer__tags__tag' anyone know how i can get it to group by tag? i've tried all the combinations of underscores in customer_tags_tag that i can think of, but nothing works.

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  • How specific do I get in BDD scenarios?

    - by CodeSpelunker
    Take two different ways of stating the same behavior. Option A: Given a customer has 50 items in their shopping cart When they check out Then they will receive a 10% discount on their order Option B: Given a customer has a high volume of items in their shopping cart When they check out Then they will receive a high volume discount on their order The former is far more specific. If someone has some question about exactly when a customer gets a high volume discount or how much to give them, reading this scenario makes it very clear. Serving the purposes of documenting the behavior, it's about as specific as it can be, although any change in those values will require changing the scenario. The second is more generalized and doesn't have the clarity of the first. Automating it would require incorporating the values "50" and "10" in the step implementations. On the other hand, the scenario captures the core business need: a high volume customer gets a discount. If we later decide to use "40" and "15", the scenario doesn't have to change because the core business need hasn't really changed (though the step implementation would). Also, the term "high volume customer" communicates something about why we're giving them the discount. So, which is better? Rather, under what circumstances should I favor the former or the latter?

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  • Entity Framework version 1- Brief Synopsis and Tips &ndash; Part 1

    - by Rohit Gupta
    To Do Eager loading use Projections (for e.g. from c in context.Contacts select c, c.Addresses)  or use Include Query Builder Methods (Include(“Addresses”)) If there is multi-level hierarchical Data then to eager load all the relationships use Include Query Builder methods like customers.Include("Order.OrderDetail") to include Order and OrderDetail collections or use customers.Include("Order.OrderDetail.Location") to include all Order, OrderDetail and location collections with a single include statement =========================================================================== If the query uses Joins then Include() Query Builder method will be ignored, use Nested Queries instead If the query does projections then Include() Query Builder method will be ignored Use Address.ContactReference.Load() OR Contact.Addresses.Load() if you need to Deferred Load Specific Entity – This will result in extra round trips to the database ObjectQuery<> cannot return anonymous types... it will return a ObjectQuery<DBDataRecord> Only Include method can be added to Linq Query Methods Any Linq Query method can be added to Query Builder methods. If you need to append a Query Builder Method (other than Include) after a LINQ method  then cast the IQueryable<Contact> to ObjectQuery<Contact> and then append the Query Builder method to it =========================================================================== Query Builder methods are Select, Where, Include Methods which use Entity SQL as parameters e.g. "it.StartDate, it.EndDate" When Query Builder methods do projection then they return ObjectQuery<DBDataRecord>, thus to iterate over this collection use contact.Item[“Name”].ToString() When Linq To Entities methods do projection, they return collection of anonymous types --- thus the collection is strongly typed and supports Intellisense EF Object Context can track changes only on Entities, not on Anonymous types. If you use a Defining Query for a EntitySet then the EntitySet becomes readonly since a Defining Query is the same as a View (which is treated as a ReadOnly by default). However if you want to use this EntitySet for insert/update/deletes then we need to map stored procs (as created in the DB) to the insert/update/delete functions of the Entity in the Designer You can use either Execute method or ToList() method to bind data to datasources/bindingsources If you use the Execute Method then remember that you can traverse through the ObjectResult<> collection (returned by Execute) only ONCE. In WPF use ObservableCollection to bind to data sources , for keeping track of changes and letting EF send updates to the DB automatically. Use Extension Methods to add logic to Entities. For e.g. create extension methods for the EntityObject class. Create a method in ObjectContext Partial class and pass the entity as a parameter, then call this method as desired from within each entity. ================================================================ DefiningQueries and Stored Procedures: For Custom Entities, one can use DefiningQuery or Stored Procedures. Thus the Custom Entity Collection will be populated using the DefiningQuery (of the EntitySet) or the Sproc. If you use Sproc to populate the EntityCollection then the query execution is immediate and this execution happens on the Server side and any filters applied will be applied in the Client App. If we use a DefiningQuery then these queries are composable, meaning the filters (if applied to the entityset) will all be sent together as a single query to the DB, returning only filtered results. If the sproc returns results that cannot be mapped to existing entity, then we first create the Entity/EntitySet in the CSDL using Designer, then create a dummy Entity/EntitySet using XML in the SSDL. When creating a EntitySet in the SSDL for this dummy entity, use a TSQL that does not return any results, but does return the relevant columns e.g. select ContactID, FirstName, LastName from dbo.Contact where 1=2 Also insure that the Entity created in the SSDL uses the SQL DataTypes and not .NET DataTypes. If you are unable to open the EDMX file in the designer then note the Errors ... they will give precise info on what is wrong. The Thrid option is to simply create a Native Query in the SSDL using <Function Name="PaymentsforContact" IsComposable="false">   <CommandText>SELECT ActivityId, Activity AS ActivityName, ImagePath, Category FROM dbo.Activities </CommandText></FuncTion> Then map this Function to a existing Entity. This is a quick way to get a custom Entity which is regular Entity with renamed columns or additional columns (which are computed columns). The disadvantage to using this is that It will return all the rows from the Defining query and any filter (if defined) will be applied only at the Client side (after getting all the rows from DB). If you you DefiningQuery instead then we can use that as a Composable Query. The Fourth option (for mapping a READ stored proc results to a non-existent Entity) is to create a View in the Database which returns all the fields that the sproc also returns, then update the Model so that the model contains this View as a Entity. Then map the Read Sproc to this View Entity. The other option would be to simply create the View and remove the sproc altogether. ================================================================ To Execute a SProc that does not return a entity, use a EntityCommand to execute that proc. You cannot call a sproc FunctionImport that does not return Entities From Code, the only way is to use SSDL function calls using EntityCommand.  This changes with EntityFramework Version 4 where you can return Scalar Types, Complex Types, Entities or NonQuery ================================================================ UDF when created as a Function in SSDL, we need to set the Name & IsComposable properties for the Function element. IsComposable is always false for Sprocs, for UDF's set this to true. You cannot call UDF "Function" from within code since you cannot import a UDF Function into the CSDL Model (with Version 1 of EF). only stored procedures can be imported and then mapped to a entity ================================================================ Entity Framework requires properties that are involved in association mappings to be mapped in all of the function mappings for the entity (Insert, Update and Delete). Because Payment has an association to Reservation... hence we need to pass both the paymentId and reservationId to the Delete sproc even though just the paymentId is the PK on the Payment Table. ================================================================ When mapping insert, update and delete procs to a Entity, insure that all the three or none are mapped. Further if you have a base class and derived class in the CSDL, then you must map (ins, upd, del) sprocs to all parent and child entities in the inheritance relationship. Note that this limitation that base and derived entity methods must all must be mapped does not apply when you are mapping Read Stored Procedures.... ================================================================ You can write stored procedures SQL directly into the SSDL by creating a Function element in the SSDL and then once created, you can map this Function to a CSDL Entity directly in the designer during Function Import ================================================================ You can do Entity Splitting such that One Entity maps to multiple tables in the DB. For e.g. the Customer Entity currently derives from Contact Entity...in addition it also references the ContactPersonalInfo Entity. One can copy all properties from the ContactPersonalInfo Entity into the Customer Entity and then Delete the CustomerPersonalInfo entity, finall one needs to map the copied properties to the ContactPersonalInfo Table in Table Mapping (by adding another table (ContactPersonalInfo) to the Table Mapping... this is called Entity Splitting. Thus now when you insert a Customer record, it will automatically create SQL to insert records into the Contact, Customers and ContactPersonalInfo tables even though you have a Single Entity called Customer in the CSDL =================================================================== There is Table by Type Inheritance where another EDM Entity can derive from another EDM entity and absorb the inherted entities properties, for example in the Break Away Geek Adventures EDM, the Customer entity derives (inherits) from the Contact Entity and absorbs all the properties of Contact entity. Thus when you create a Customer Entity in Code and then call context.SaveChanges the Object Context will first create the TSQL to insert into the Contact Table followed by a TSQL to insert into the Customer table =================================================================== Then there is the Table per Hierarchy Inheritance..... where different types are created based on a condition (similar applying a condition to filter a Entity to contain filtered records)... the diference being that the filter condition populates a new Entity Type (derived from the base Entity). In the BreakAway sample the example is Lodging Entity which is a Abstract Entity and Then Resort and NonResort Entities which derive from Lodging Entity and records are filtered based on the value of the Resort Boolean field =================================================================== Then there is Table per Concrete Type Hierarchy where we create a concrete Entity for each table in the database. In the BreakAway sample there is a entity for the Reservation table and another Entity for the OldReservation table even though both the table contain the same number of fields. The OldReservation Entity can then inherit from the Reservation Entity and configure the OldReservation Entity to remove all Scalar Properties from the Entity (since it inherits the properties from Reservation and filters based on ReservationDate field) =================================================================== Complex Types (Complex Properties) Entities in EF can also contain Complex Properties (in addition to Scalar Properties) and these Complex Properties reference a ComplexType (not a EntityType) DropdownList, ListBox, RadioButtonList, CheckboxList, Bulletedlist are examples of List server controls (not data bound controls) these controls cannot use Complex properties during databinding, they need Scalar Properties. So if a Entity contains Complex properties and you need to bind those to list server controls then use projections to return Scalar properties and bind them to the control (the disadvantage is that projected collections are not tracked by the Object Context and hence cannot persist changes to the projected collections bound to controls) ObjectDataSource and EntityDataSource do account for Complex properties and one can bind entities with Complex Properties to Data Source controls and they will be tracked for changes... with no additional plumbing needed to persist changes to these collections bound to controls So DataBound controls like GridView, FormView need to use EntityDataSource or ObjectDataSource as a datasource for entities that contain Complex properties so that changes to the datasource done using the GridView can be persisted to the DB (enabling the controls for updates)....if you cannot use the EntityDataSource you need to flatten the ComplexType Properties using projections With EF Version 4 ComplexTypes are supported by the Designer and can add/remove/compose Complex Types directly using the Designer =================================================================== Conditional Mapping ... is like Table per Hierarchy Inheritance where Entities inherit from a base class and then used conditions to populate the EntitySet (called conditional Mapping). Conditional Mapping has limitations since you can only use =, is null and IS NOT NULL Conditions to do conditional mapping. If you need more operators for filtering/mapping conditionally then use QueryView(or possibly Defining Query) to create a readonly entity. QueryView are readonly by default... the EntitySet created by the QueryView is enabled for change tracking by the ObjectContext, however the ObjectContext cannot create insert/update/delete TSQL statements for these Entities when SaveChanges is called since it is QueryView. One way to get around this limitation is to map stored procedures for the insert/update/delete operations in the Designer. =================================================================== Difference between QueryView and Defining Query : QueryView is defined in the (MSL) Mapping File/section of the EDM XML, whereas the DefiningQuery is defined in the store schema (SSDL). QueryView is written using Entity SQL and is this database agnostic and can be used against any database/Data Layer. DefiningQuery is written using Database Lanaguage i.e. TSQL or PSQL thus you have more control =================================================================== Performance: Lazy loading is deferred loading done automatically. lazy loading is supported with EF version4 and is on by default. If you need to turn it off then use context.ContextOptions.lazyLoadingEnabled = false To improve Performance consider PreCompiling the ObjectQuery using the CompiledQuery.Compile method

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  • eBooks on iPad vs. Kindle: More Debate than Smackdown

    - by andrewbrust
    When the iPad was presented at its San Francisco launch event on January 28th, Steve Jobs spent a significant amount of time explaining how well the device would serve as an eBook reader. He showed the iBooks reader application and iBookstore and laid down the gauntlet before Amazon and its beloved Kindle device. Almost immediately afterwards, criticism came rushing forth that the iPad could never beat the Kindle for book reading. The curious part of that criticism is that virtually no one offering it had actually used the iPad yet. A few weeks later, on April 3rd, the iPad was released for sale in the United States. I bought one on that day and in the few additional weeks that have elapsed, I’ve given quite a workout to most of its capabilities, including its eBook features. I’ve also spent some time with the Kindle, albeit a first-generation model, to see how it actually compares to the iPad. I had some expectations going in, but I came away with conclusions about each device that were more scenario-based than absolute. I present my findings to you here.   Vital Statistics Let’s start with an inventory of each device’s underlying technology. The iPad has a color, backlit LCD screen and an on-screen keyboard. It has a battery which, on a full charge, lasts anywhere from 6-10 hours. The Kindle offers a monochrome, reflective E Ink display, a physical keyboard and a battery that on my first gen loaner unit can go up to a week between charges (Amazon claims the battery on the Kindle 2 can last up to 2 weeks on a single charge). The Kindle connects to Amazon’s Kindle Store using a 3G modem (the technology and network vary depending on the model) that incurs no airtime service charges whatsoever. The iPad units that are on-sale today work over WiFi only. 3G-equipped models will be on sale shortly and will command a $130 premium over their WiFi-only counterparts. 3G service on the iPad, in the U.S. from AT&T, will be fee-based, with a 250MB plan at $14.99 per month and an unlimited plan at $29.99. No contract is required for 3G service. All these tech specs aside, I think a more useful observation is that the iPad is a multi-purpose Internet-connected entertainment device, while the Kindle is a dedicated reading device. The question is whether those differences in design and intended use create a clear-cut winner for reading electronic publications. Let’s take a look at each device, in isolation, now.   Kindle To me, what’s most innovative about the Kindle is its E Ink display. E Ink really looks like ink on a sheet of paper. It requires no backlight, it’s fully visible in direct sunlight and it causes almost none of the eyestrain that LCD-based computer display technology (like that used on the iPad) does. It’s really versatile in an all-around way. Forgive me if this sounds precious, but reading on it is really a joy. In fact, it’s a genuinely relaxing experience. Through the Kindle Store, Amazon allows users to download books (including audio books), magazines, newspapers and blog feeds. Books and magazines can be purchased either on a single-issue basis or as an annual subscription. Books, of course, are purchased singly. Oddly, blogs are not free, but instead carry a monthly subscription fee, typically $1.99. To me this is ludicrous, but I suppose the free 3G service is partially to blame. Books and magazine issues download quickly. Magazine and blog subscriptions cause new issues or posts to be pushed to your device on an automated basis. Available blogs include 9000-odd feeds that Amazon offers on the Kindle Store; unless I missed something, arbitrary RSS feeds are not supported (though there are third party workarounds to this limitation). The shopping experience is integrated well, has an huge selection, and offers certain graphical perks. For example, magazine and newspaper logos are displayed in menus, and book cover thumbnails appear as well. A simple search mechanism is provided and text entry through the physical keyboard is relatively painless. It’s very easy and straightforward to enter the store, find something you like and start reading it quickly. If you know what you’re looking for, it’s even faster. Given Kindle’s high portability, very reliable battery, instant-on capability and highly integrated content acquisition, it makes reading on whim, and in random spurts of downtime, very attractive. The Kindle’s home screen lists all of your publications, and easily lets you select one, then start reading it. Once opened, publications display in crisp, attractive text that is adjustable in size. “Turning” pages is achieved through buttons dedicated to the task. Notes can be recorded, bookmarks can be saved and pages can be saved as clippings. I am not an avid book reader, and yet I found the Kindle made it really fun, convenient and soothing to read. There’s something about the easy access to the material and the simplicity of the display that makes the Kindle seduce you into chilling out and reading page after page. On the other hand, the Kindle has an awkward navigation interface. While menus are displayed clearly on the screen, the method of selecting menu items is tricky: alongside the right-hand edge of the main display is a thin column that acts as a second display. It has a white background, and a scrollable silver cursor that is moved up or down through the use of the device’s scrollwheel. Picking a menu item on the main display involves scrolling the silver cursor to a position parallel to that menu item and pushing the scrollwheel in. This navigation technique creates a disconnect, literally. You don’t really click on a selection so much as you gesture toward it. I got used to this technique quickly, but I didn’t love it. It definitely created a kind of anxiety in me, making me feel the need to speed through menus and get to my destination document quickly. Once there, I could calm down and relax. Books are great on the Kindle. Magazines and newspapers much less so. I found the rendering of photographs, and even illustrations, to be unacceptably crude. For this reason, I expect that reading textbooks on the Kindle may leave students wanting. I found that the original flow and layout of any publication was sacrificed on the Kindle. In effect, browsing a magazine or newspaper was almost impossible. Reading the text of individual articles was enjoyable, but having to read this way made the whole experience much more “a la carte” than cohesive and thematic between articles. I imagine that for academic journals this is ideal, but for consumer publications it imposes a stripped-down, low-fidelity experience that evokes a sense of deprivation. In general, the Kindle is great for reading text. For just about anything else, especially activity that involves exploratory browsing, meandering and short-attention-span reading, it presents a real barrier to entry and adoption. Avid book readers will enjoy the Kindle (if they’re not already). It’s a great device for losing oneself in a book over long sittings. Multitaskers who are more interested in periodicals, be they online or off, will like it much less, as they will find compromise, and even sacrifice, to be palpable.   iPad The iPad is a very different device from the Kindle. While the Kindle is oriented to pages of text, the iPad orbits around applications and their interfaces. Be it the pinch and zoom experience in the browser, the rich media features that augment content on news and weather sites, or the ability to interact with social networking services like Twitter, the iPad is versatile. While it shares a slate-like form factor with the Kindle, it’s effectively an elegant personal computer. One of its many features is the iBook application and integration of the iBookstore. But it’s a multi-purpose device. That turns out to be good and bad, depending on what you’re reading. The iBookstore is great for browsing. It’s color, rich animation-laden user interface make it possible to shop for books, rather than merely search and acquire them. Unfortunately, its selection is rather sparse at the moment. If you’re looking for a New York Times bestseller, or other popular titles, you should be OK. If you want to read something more specialized, it’s much harder. Unlike the awkward navigation interface of the Kindle, the iPad offers a nearly flawless touch-screen interface that seduces the user into tinkering and kibitzing every bit as much as the Kindle lulls you into a deep, concentrated read. It’s a dynamic and interactive device, whereas the Kindle is static and passive. The iBook reader is slick and fun. Use the iPad in landscape mode and you can read the book in 2-up (left/right 2-page) display; use it in portrait mode and you can read one page at a time. Rather than clicking a hardware button to turn pages, you simply drag and wipe from right-to-left to flip the single or right-hand page. The page actually travels through an animated path as it would in a physical book. The intuitiveness of the interface is uncanny. The reader also accommodates saving of bookmarks, searching of the text, and the ability to highlight a word and look it up in a dictionary. Pages display brightly and clearly. They’re easy to read. But the backlight and the glare made me less comfortable than I was with the Kindle. The knowledge that completely different applications (including the Web and email and Twitter) were just a few taps away made me antsy and very tempted to task-switch. The knowledge that battery life is an issue created subtle discomfort. If the Kindle makes you feel like you’re in a library reading room, then the iPad makes you feel, at best, like you’re under fluorescent lights at a Barnes and Noble or Borders store. If you’re lucky, you’d be on a couch or at a reading table in the store, but you might also be standing up, in the aisles. Clearly, I didn’t find this conducive to focused and sustained reading. But that may have more to do with my own tendency to read periodicals far more than books, and my neurotic . And, truth be known, the book reading experience, when not explicitly compared to Kindle’s, was still pleasant. It is also important to point out that Kindle Store-sourced books can be read on the iPad through a Kindle reader application, from Amazon, specific to the device. This offered a less rich experience than the iBooks reader, but it was completely adequate. Despite the Kindle brand of the reader, however, it offered little in terms of simulating the reading experience on its namesake device. When it comes to periodicals, the iPad wins hands down. Magazines, even if merely scanned images of their print editions, read on the iPad in a way that felt similar to reading hard copy. The full color display, touch navigation and even the ability to render advertisements in their full glory makes the iPad a great way to read through any piece of work that is measured in pages, rather than chapters. There are many ways to get magazines and newspapers onto the iPad, including the Zinio reader, and publication-specific applications like the Wall Street Journal’s and Popular Science’s. The New York Times’ free Editors’ Choice application offers a Times Reader-like interface to a subset of the Gray Lady’s daily content. The completely Web-based but iPad-optimized Times Skimmer site (at www.nytimes.com/timesskimmer) works well too. Even conventional Web sites themselves can be read much like magazines, given the iPad’s ability to zoom in on the text and crop out advertisements on the margins. While the Kindle does have an experimental Web browser, it reminded me a lot of early mobile phone browsers, only in a larger size. For text-heavy sites with simple layout, it works fine. For just about anything else, it becomes more trouble than it’s worth. And given the way magazine articles make me think of things I want to look up online, I think that’s a real liability for the Kindle.   Summing Up What I came to realize is that the Kindle isn’t so much a computer or even an Internet device as it is a printer. While it doesn’t use physical paper, it still renders its content a page at a time, just like a laser printer does, and its output appears strikingly similar. You can read the rendered text, but you can’t interact with it in any way. That’s why the navigation requires a separate cursor display area. And because of the page-oriented rendering behavior, turning pages causes a flash on the display and requires a sometimes long pause before the next page is rendered. The good side of this is that once the page is generated, no battery power is required to display it. That makes for great battery life, optimal viewing under most lighting conditions (as long as there is some light) and low-eyestrain text-centric display of content. The Kindle is highly portable, has an excellent selection in its store and is refreshingly distraction-free. All of this is ideal for reading books. And iPad doesn’t offer any of it. What iPad does offer is versatility, variety, richness and luxury. It’s flush with accoutrements even if it’s low on focused, sustained text display. That makes it inferior to the Kindle for book reading. But that also makes it better than the Kindle for almost everything else. As such, and given that its book reading experience is still decent (even if not superior), I think the iPad will give Kindle a run for its money. True book lovers, and people on a budget, will want the Kindle. People with a robust amount of discretionary income may want both devices. Everyone else who is interested in a slate form factor e-reading device, especially if they also wish to have leisure-friendly Internet access, will likely choose the iPad exclusively. One thing is for sure: iPad has reduced Kindle’s market, and may have shifted its mass market potential to a mere niche play. If Amazon is smart, it will improve its iPad-based Kindle reader app significantly. It can then leverage the iPad channel as a significant market for the Kindle Store. After all, selling the eBooks themselves is what Amazon should care most about.

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