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• Is there really Object-relational impedance mismatch?

  - by user52763

  It is always stated that it is hard to store applications objects in relational databases - the object-relational impedance mismatch - and that is why Document databases are better. However, is there really an impedance mismatch? And object has a key (albeit it may be hidden away by the runtime as a pointer to memory), a set of values, and foreign keys to other objects. Objects are as much made up of tables as it is a document. Neither really fit. I can see a use for databases to model the data into specific shapes for scenarios in the application - e.g. to speed up database lookup and avoid joins, etc., but won't it be better to keep the data as normalized as possible at the core, and transform as required?

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• Architecture Best Practice (MVC): Repository Returns Object & Object Member Accessed Directly or Repository Returns Object Member

  - by coderabbi

  Architecturally speaking, which is the preferable approach (and why)? $validation_date = $users_repository->getUser($user_id)->validation_date; Seems to violate Law of Demeter by accessing member of object returned by method call Seems to violate Encapsulation by accessing object member directly $validation_date = $users_repository->getUserValidationDate($user_id); Seems to violate Single Responsibility Principle as $users_repository no longer just returns User objects

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• Start a Mapping or Process Flow from OWB Browser

  - by Dong Ruirong

  Basically, we start a Mapping or Process Flow from Oracle Warehouse Builder (OWB) Design Client. But actually we can also start a Mapping or Process Flow from OWB Browser. This paper will introduce the Start Report first and then introduce how to start/rerun a Mapping or Process Flow from OWB Browser. Start Report Start Report is used to start an execution of a Mapping or Process Flow. So there are two kinds of Start Report: Mapping Start Report (See Figure 1) and Process Flow Start Report (See Figure 2). Start Report shows the Mapping or Process Flow identification properties, including latest deployment and latest execution, lists all execution parameters for the Mapping or Process Flow, which were specified by the latest deployment, and assigns parameter default values from the latest deployment specification. You can do a couple of things from Start Report: Sort execution parameters on name, category. Table 1 lists all parameters of a Mapping. Table 2 lists all parameters of a Process Flow. Change values of any input parameter where permitted. For some parameters, selection lists are provided. For example, Mapping’s parameter Audit Level has a selection list. Reset all parameter settings to their default values. Apply basic validation to parameter values before starting an execution. Start the Mapping or Process Flow, which means it is executed immediately. Navigate to Deployment Report for latest deployment details of the Mapping or Process Flow. Navigate to Execution Job Report for latest execution of current Mapping or Process Flow Link to on-link help Warehouse Report Page, Deployment Report, Execution Report, Execution Schedule Report and Execution Summary Report. Figure 1 Mapping Start Report Table 1 Execution Parameters and default values for a Mapping Category Name Mode Input Value System Audit Level In Error Details System Bulk Size In 1000 System Commit Frequency In 1000 System EXECUTE_RESUME_TASK In FALSE System FORCE_RESUME_OPTION In FALSE System Max No of Errors In 50 System NUMBER_OF_TIMES_TO_RETRY In 2 System Operating Mode In Set Based Fail Over to Row Based System PARALLEL_LEVEL In 0 System Procedure Name In main System Purge Group In WB Figure 2 Process Flow Start Report Table 2 Execution Parameters and default values for a Process Flow Category Name Mode Input Value System EVAL_LOCATION In   System Item Key In-Out   System Item Type In PFPKG_1 Start a Mapping or Process Flow To navigate to Start Report, it’s better to login OWB Browser with Control Center option; if not, after logging in OWB Browser, go to Control Center first. Then you can follow the ways introduced in this section to navigate to Start Report. One more thing you need to pay attention to is that you are not allowed to deploy any Mappings and Process Flows from OWB Browser as it’s not supported. So it’s necessary to deploy the Mappings and Process Flows first before starting them from OWB Browser. If you have deployed a Mapping or Process Flow but have not started it, please navigate from Object Summary Report or Deployment Schedule Report to Start Report. 1. Navigating from Object Summary Report to Start Report Open the Object Summary Report to see all deployed Mappings and Process Flows. Click the Mapping Name or Process Flow Name link to see its Deployment Report. Select the Start link in the Available Reports tab for the given Mapping or Process Flow to display a Start Report for the Mapping or Process Flow. The execution parameters have the default deployment-time settings. Change any of the input parameter values as required. Click Start Execution button to execute the Mapping or Process Flow. 2. Navigating from Deployment Schedule Report to Start Report Open the Deployment Schedule Report to see deployment details of Mapping and Process Flow. Expand the project trees to find the deployed Mappings and Process Flows. Click the Mapping Name or Process Flow Name link to see its Deployment Report. Select the Start link in the Available Reports tab for the given Mapping or Process Flow to display a Start Report for the Mapping or Process Flow. The execution parameters have the default deployment-time settings. Change any of the input parameter values as required. Click Start Execution button to execute the Mapping or Process Flow. Re-run a Mapping or Process Flow If you have executed a Mapping or Process Flow, you can navigate from Object Summary Report, Deployment Schedule Report, Execution Summary Report or Execution Schedule Report to Start Report. 1. Navigating from the Execution Summary Report to Start Report Open the Execution Summary Report to see all execution jobs including Mapping jobs and Process Flow jobs. Click on the Mapping Name or Process Flow Name to see its Execution Report. Select the Start link in the Available Reports tab for the given Mapping or Process Flow to display a Start Report for the Mapping or Process Flow. The execution parameters have the default deployment-time settings. Change any of the input parameter values as required. Click Start Execution button to execute the Mapping or Process Flow. 2. Navigating from the Execution Schedule Report to Start Report Open the Execution Schedule Report to see list of all executions of Mapping and Process Flow. Click on the Mapping Name or Process Flow Name to see its Execution Report. Select the Start link in the Available Reports tab for the given Mapping or Process Flow to display a Start Report for the Mapping or Process Flow. The execution parameters have the default deployment-time settings. Change any of the input parameter values as required. Click Start Execution button to execute the Mapping or Process Flow. If the execution of a Mapping or Process Flow is successful, you will see this message from the Start Report: Start Execution request successful. (See Figure 3) Figure 3 Execution Result You can also confirm the execution of the Mapping or Process Flow by referring to Execution Report of the current Mapping or Process Flow by clicking the link in the Available Reports tab for the given Mapping or Process Flow. One new record of execution job details is added to Execution Report of the Mapping or Process Flow which shows the details of the execution such as Start Time, Elapsed Time, Status, the number of records selected, inserted, updated, deleted etc.

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• Working with Temporal Data in SQL Server

  - by Dejan Sarka

  My third Pluralsight course, Working with Temporal Data in SQL Server, is published. I am really proud on the second part of the course, where I discuss optimization of temporal queries. This was a nearly impossible task for decades. First solutions appeared only lately. I present all together six solutions (and one more that is not a solution), and I invented four of them. http://pluralsight.com/training/Courses/TableOfContents/working-with-temporal-data-sql-server

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• When would you want two references to the same object?

  - by HCBPshenanigans

  In Java specifically, but likely in other languages as well; When would it be useful to have two references to the same object? Example: Dog a = new Dog(); Dob b = a; Is there a situation where this would be useful? Why would this be a preferred solution to using a whenever you want to interact with the object represented by a? Edit: Can I just say that all of your dog related examples are Delightful!

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• The Best Websites and Software for Brainstorming and Mind Mapping

  - by Lori Kaufman

  A mind map is a diagram that allows you to visually outline information, helping you organize, solve problems, and make decisions. Start with a single idea in the center of the diagram and add associated ideas, words, and concepts connected radially around the central idea. We’ve collected links to websites and software that can help you create mind maps, and collaborate on and share your maps with others. The programs and websites listed here are all either free or have a free option. How To Delete, Move, or Rename Locked Files in Windows HTG Explains: Why Screen Savers Are No Longer Necessary 6 Ways Windows 8 Is More Secure Than Windows 7

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• Chris Date on "SQL and Relational Theory - How to Write Accurate SQL Code"

  - by MartinBell

  The importance of relational theory......(read more)

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• Big Data – Buzz Words: Importance of Relational Database in Big Data World – Day 9 of 21

  - by Pinal Dave

  In yesterday’s blog post we learned what is HDFS. In this article we will take a quick look at the importance of the Relational Database in Big Data world. A Big Question? Here are a few questions I often received since the beginning of the Big Data Series - Does the relational database have no space in the story of the Big Data? Does relational database is no longer relevant as Big Data is evolving? Is relational database not capable to handle Big Data? Is it true that one no longer has to learn about relational data if Big Data is the final destination? Well, every single time when I hear that one person wants to learn about Big Data and is no longer interested in learning about relational database, I find it as a bit far stretched. I am not here to give ambiguous answers of It Depends. I am personally very clear that one who is aspiring to become Big Data Scientist or Big Data Expert they should learn about relational database. NoSQL Movement The reason for the NoSQL Movement in recent time was because of the two important advantages of the NoSQL databases. Performance Flexible Schema In personal experience I have found that when I use NoSQL I have found both of the above listed advantages when I use NoSQL database. There are instances when I found relational database too much restrictive when my data is unstructured as well as they have in the datatype which my Relational Database does not support. It is the same case when I have found that NoSQL solution performing much better than relational databases. I must say that I am a big fan of NoSQL solutions in the recent times but I have also seen occasions and situations where relational database is still perfect fit even though the database is growing increasingly as well have all the symptoms of the big data. Situations in Relational Database Outperforms Adhoc reporting is the one of the most common scenarios where NoSQL is does not have optimal solution. For example reporting queries often needs to aggregate based on the columns which are not indexed as well are built while the report is running, in this kind of scenario NoSQL databases (document database stores, distributed key value stores) database often does not perform well. In the case of the ad-hoc reporting I have often found it is much easier to work with relational databases. SQL is the most popular computer language of all the time. I have been using it for almost over 10 years and I feel that I will be using it for a long time in future. There are plenty of the tools, connectors and awareness of the SQL language in the industry. Pretty much every programming language has a written drivers for the SQL language and most of the developers have learned this language during their school/college time. In many cases, writing query based on SQL is much easier than writing queries in NoSQL supported languages. I believe this is the current situation but in the future this situation can reverse when No SQL query languages are equally popular. ACID (Atomicity Consistency Isolation Durability) – Not all the NoSQL solutions offers ACID compliant language. There are always situations (for example banking transactions, eCommerce shopping carts etc.) where if there is no ACID the operations can be invalid as well database integrity can be at risk. Even though the data volume indeed qualify as a Big Data there are always operations in the application which absolutely needs ACID compliance matured language. The Mixed Bag I have often heard argument that all the big social media sites now a days have moved away from Relational Database. Actually this is not entirely true. While researching about Big Data and Relational Database, I have found that many of the popular social media sites uses Big Data solutions along with Relational Database. Many are using relational databases to deliver the results to end user on the run time and many still uses a relational database as their major backbone. Here are a few examples: Facebook uses MySQL to display the timeline. (Reference Link) Twitter uses MySQL. (Reference Link) Tumblr uses Sharded MySQL (Reference Link) Wikipedia uses MySQL for data storage. (Reference Link) There are many for prominent organizations which are running large scale applications uses relational database along with various Big Data frameworks to satisfy their various business needs. Summary I believe that RDBMS is like a vanilla ice cream. Everybody loves it and everybody has it. NoSQL and other solutions are like chocolate ice cream or custom ice cream – there is a huge base which loves them and wants them but not every ice cream maker can make it just right  for everyone’s taste. No matter how fancy an ice cream store is there is always plain vanilla ice cream available there. Just like the same, there are always cases and situations in the Big Data’s story where traditional relational database is the part of the whole story. In the real world scenarios there will be always the case when there will be need of the relational database concepts and its ideology. It is extremely important to accept relational database as one of the key components of the Big Data instead of treating it as a substandard technology. Ray of Hope – NewSQL In this module we discussed that there are places where we need ACID compliance from our Big Data application and NoSQL will not support that out of box. There is a new termed coined for the application/tool which supports most of the properties of the traditional RDBMS and supports Big Data infrastructure – NewSQL. Tomorrow In tomorrow’s blog post we will discuss about NewSQL. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• Need help with NHibernate / Fluent NHibernate mapping

  - by Mark Boltuc

  Let's say your have the following table structure: ============================== | Case | ============================== | Id | int | | ReferralType | varchar(10) | +---------| ReferralId | int |---------+ | ============================== | | | | | | | ====================== ====================== ====================== | SourceA | | SourceB | | SourceC | ====================== ====================== ====================== | Id | int | | Id | int | | Id | int | | Name | varchar(50) | | Name | varchar(50) | | Name | varchar(50) | ====================== ====================== ====================== Based on the ReferralType the ReferralId contains id to the SourceA, SourceB, or SourceC I'm trying to figure out how to map this using Fluent NHibernate or just plain NHibernate into an object model. I've tried a bunch of different things but I haven't been succesful. Any ideas? The object model might be something like: public class Case { public int Id { get; set; } public Referral { get; set; } } public class Referral { public string Type { get; set; } public int Id { get; set; } public string Name { get; set; } }

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• ODI 12c's Mapping Designer - Combining Flow Based and Expression Based Mapping

  - by Madhu Nair

  post by David Allan ODI is renowned for its declarative designer and minimal expression based paradigm. The new ODI 12c release has extended this even further to provide an extended declarative mapping designer. The ODI 12c mapper is a fusion of ODI's new declarative designer with the familiar flow based designer while retaining ODI’s key differentiators of: Minimal expression based definition, The ability to incrementally design an interface and to extract/load data from any combination of sources, and most importantly Backed by ODI’s extensible knowledge module framework. The declarative nature of the product has been extended to include an extensible library of common components that can be used to easily build simple to complex data integration solutions. Big usability improvements through consistent interactions of components and concepts all constructed around the familiar knowledge module framework provide the utmost flexibility. Here is a little taster: So what is a mapping? A mapping comprises of a logical design and at least one physical design, it may have many. A mapping can have many targets, of any technology and can be arbitrarily complex. You can build reusable mappings and use them in other mappings or other reusable mappings. In the example below all of the information from an Oracle bonus table and a bonus file are joined with an Oracle employees table before being written to a target. Some things that are cool include the one-click expression cross referencing so you can easily see what's used where within the design. The logical design in a mapping describes what you want to accomplish  (see the animated GIF here illustrating how the above mapping was designed) . The physical design lets you configure how it is to be accomplished. So you could have one logical design that is realized as an initial load in one physical design and as an incremental load in another. In the physical design below we can customize how the mapping is accomplished by picking Knowledge Modules, in ODI 12c you can pick multiple nodes (on logical or physical) and see common properties. This is useful as we can quickly compare property values across objects - below we can see knowledge modules settings on the access points between execution units side by side, in the example one table is retrieved via database links and the other is an external table. In the logical design I had selected an append mode for the integration type, so by default the IKM on the target will choose the most suitable/default IKM - which in this case is an in-built Oracle Insert IKM (see image below). This supports insert and select hints for the Oracle database (the ANSI SQL Insert IKM does not support these), so by default you will get direct path inserts with Oracle on this statement. In ODI 12c, the mapper is just that, a mapper. Design your mapping, write to multiple targets, the targets can be in the same data server, in different data servers or in totally different technologies - it does not matter. ODI 12c will derive and generate a plan that you can use or customize with knowledge modules. Some of the use cases which are greatly simplified include multiple heterogeneous targets, multi target inserts for Oracle and writing of XML. Let's switch it up now and look at a slightly different example to illustrate expression reuse. In ODI you can define reusable expressions using user functions. These can be reused across mappings and the implementations specialized per technology. So you can have common expressions across Oracle, SQL Server, Hive etc. shielding the design from the physical aspects of the generated language. Another way to reuse is within a mapping itself. In ODI 12c expressions can be defined and reused within a mapping. Rather than replicating the expression text in larger expressions you can decompose into smaller snippets, below you can see UNIT_TAX AMOUNT has been defined and is used in two downstream target columns - its used in the TOTAL_TAX_AMOUNT plus its used in the UNIT_TAX_AMOUNT (a recording of the calculation).  You can see the columns that the expressions depend on (upstream) and the columns the expression is used in (downstream) highlighted within the mapper. Also multi selecting attributes is a convenient way to see what's being used where, below I have selected the TOTAL_TAX_AMOUNT in the target datastore and the UNIT_TAX_AMOUNT in UNIT_CALC. You can now see many expressions at once now and understand much more at the once time without needlessly clicking around and memorizing information. Our mantra during development was to keep it simple and make the tool more powerful and do even more for the user. The development team was a fusion of many teams from Oracle Warehouse Builder, Sunopsis and BEA Aqualogic, debating and perfecting the mapper in ODI 12c. This was quite a project from supporting the capabilities of ODI in 11g to building the flow based mapping tool to support the future. I hope this was a useful insight, there is so much more to come on this topic, this is just a preview of much more that you will see of the mapper in ODI 12c.

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• How to safely copy an object?

  - by Prog

  This question is going to be a little long. Please bear with me. Something that happened in a project of mine made me think about how to safely copy objects. I'll present the situation I had and then ask a question. There was a class SomeClass: class SomeClass{ Thing[] things; public SomeClass(Thing[] things){ this.things = things; } // irrelevant stuff omitted public SomeClass copy(){ return new SomeClass(things); } } There was another class Processor that takes SomeClass objects, copies them (via someClassInstance.copy()), manipulates the copy's state, and returns the copy. Here it is: class Processor{ public SomeClass processObject(SomeClass object){ SomeClass copy = object.copy(); manipulateTheCopy(copy); return copy; } // irrelevant stuff omitted } I ran this, and it had bugs. I looked into these bugs, and it turned out that the manipulations Processor does on copy actually affect not only the copy, but also the original SomeClass object that was passed into processObject. I found out that it was because the original and the copy shared state - because the original passed it's field things into the copy when creating it. This made me realize that copying objects is harder than simply instantiating them with the same fields as the original. For the two objects to be completely disconnected, without any shared state, each of the fields passed to the copy also has to be copied. And if that object contains other objects - they have to be copied too. And so on. So basically, in order to be able to actually copy an object, each class in the system must have a copy() method, that also invokes copy() on all of it's fields, and so on. So for example, for copy() in SomeClass to work, it needs to look like this: public SomeClass copy(){ Thing[] copyThings = new Thing[things.length]; for(int i=0; i<things.length; i++) copyThings[i] = things[i].copy(); return new SomeClass(copyThings); } And if Thing has object fields of it's own, than it's own copy() method must be appropriate: class Thing{ Apple apple; Pencil pencil; int number; public Thing(Apple apple, Pencil pencil, int number){ this.apple = apple; this.pencil = pencil; this.number = number; } public Thing copy(){ // 'number' is a primitve. return new Thing(apple.getCopy(), pencil.getCopy(), number); } } And so on. Of course, instead of all classes having a copy() method, the copying mechanism can happen in all of the getters and the constructors of classes (unless places where it isn't suitable, for example when the field points to an external object, not to an object that 'is part' of this object). Still, that means that in order to be able to safely copy an object - most classes would have to have copying mechanisms in their getters. My question is divided into two parts: How frequently do you need to get a copy of an object? Is this a regular issue? Is the technique described common and/or reasonable? Or is there a better way to make safe copies of objects? Or is there an easier way to safely copy objects, without them sharing any state?

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• Is it easy to switch from relational to non-relational databases with Rails?

  - by Tam

  Good day, I have been using Rails/Mysql for the past while but I have been hearing about Cassandra, MongoDB, CouchDB and other document-store DB/Non-relational databases. I'm planning to explore them later as they might be better alternative for scalability. I'm planning to start an application soon. Will it make a different with Rails design if I move from relational to non-relational database? I know Rails migrations are database-agnostic but wasn't sure if moving to non-relational will make difference with design or not.

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• Should an object know its own ID?

  - by xenoterracide

  obj.id seems fairly common and also seems to fall within the range of something an object could know about itself. I find myself asking why should my object know its own id? It doesn't seem to have a reason to have it? One of the main reason for it existing is retrieve it, and so my repositories need to know it, and thus use it for database interaction. I also once encountered a problem where I wanted to serialize an object to JSON for a RESTful API where the id did not seem to fit in the payload, but only the URI and including it in the object made that more difficult. Should an object know it's own id? why or why not?

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• Object oriented design importance

  - by user5507

  I started studying Object Oriented Design and Modelling using the this book by James Rumbaugh. It uses a tool called Object Modeling Technique (OMT). I have certain newbie questions. I searched the net, but couldn't get answers The book is pretty old. Don't know why the school told me to learn this. I know OMT is a predecessor of the Unified Modeling Language (UML). So its a waste? Whether the concepts change very much when we move from OMT to UML? I know OMT has Object, Dynamic and Functional Model. Wikipedia says UML is compatible with OMT and UML is a model too. As per wikipedia the UML models are Static and Dynamic and they are represented by different diagrams like class, object, activity, sequence..... I couldn't find the equivalence of this in OMT. I read that there are many object oriented development methods like OMT, Booch,.... Which one is used by Industry ? Where could I get a comparison of different Object oriented development methods?

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• Entity Association Mapping with Code First Part 1 : Mapping Complex Types

  - by mortezam

  Last week the CTP5 build of the new Entity Framework Code First has been released by data team at Microsoft. Entity Framework Code-First provides a pretty powerful code-centric way to work with the databases. When it comes to associations, it brings ultimate flexibility. I’m a big fan of the EF Code First approach and am planning to explain association mapping with code first in a series of blog posts and this one is dedicated to Complex Types. If you are new to Code First approach, you can find a great walkthrough here. In order to build a solid foundation for our discussion, we will start by learning about some of the core concepts around the relationship mapping.   What is Mapping?Mapping is the act of determining how objects and their relationships are persisted in permanent data storage, in our case, relational databases. What is Relationship mapping?A mapping that describes how to persist a relationship (association, aggregation, or composition) between two or more objects. Types of RelationshipsThere are two categories of object relationships that we need to be concerned with when mapping associations. The first category is based on multiplicity and it includes three types: One-to-one relationships: This is a relationship where the maximums of each of its multiplicities is one. One-to-many relationships: Also known as a many-to-one relationship, this occurs when the maximum of one multiplicity is one and the other is greater than one. Many-to-many relationships: This is a relationship where the maximum of both multiplicities is greater than one. The second category is based on directionality and it contains two types: Uni-directional relationships: when an object knows about the object(s) it is related to but the other object(s) do not know of the original object. To put this in EF terminology, when a navigation property exists only on one of the association ends and not on the both. Bi-directional relationships: When the objects on both end of the relationship know of each other (i.e. a navigation property defined on both ends). How Object Relationships Are Implemented in POCO domain models?When the multiplicity is one (e.g. 0..1 or 1) the relationship is implemented by defining a navigation property that reference the other object (e.g. an Address property on User class). When the multiplicity is many (e.g. 0..*, 1..*) the relationship is implemented via an ICollection of the type of other object. How Relational Database Relationships Are Implemented? Relationships in relational databases are maintained through the use of Foreign Keys. A foreign key is a data attribute(s) that appears in one table and must be the primary key or other candidate key in another table. With a one-to-one relationship the foreign key needs to be implemented by one of the tables. To implement a one-to-many relationship we implement a foreign key from the “one table” to the “many table”. We could also choose to implement a one-to-many relationship via an associative table (aka Join table), effectively making it a many-to-many relationship. Introducing the ModelNow, let's review the model that we are going to use in order to implement Complex Type with Code First. It's a simple object model which consist of two classes: User and Address. Each user could have one billing address. The Address information of a User is modeled as a separate class as you can see in the UML model below: In object-modeling terms, this association is a kind of aggregation—a part-of relationship. Aggregation is a strong form of association; it has some additional semantics with regard to the lifecycle of objects. In this case, we have an even stronger form, composition, where the lifecycle of the part is fully dependent upon the lifecycle of the whole. Fine-grained domain models The motivation behind this design was to achieve Fine-grained domain models. In crude terms, fine-grained means “more classes than tables”. For example, a user may have both a billing address and a home address. In the database, you may have a single User table with the columns BillingStreet, BillingCity, and BillingPostalCode along with HomeStreet, HomeCity, and HomePostalCode. There are good reasons to use this somewhat denormalized relational model (performance, for one). In our object model, we can use the same approach, representing the two addresses as six string-valued properties of the User class. But it’s much better to model this using an Address class, where User has the BillingAddress and HomeAddress properties. This object model achieves improved cohesion and greater code reuse and is more understandable. Complex Types: Splitting a Table Across Multiple Types Back to our model, there is no difference between this composition and other weaker styles of association when it comes to the actual C# implementation. But in the context of ORM, there is a big difference: A composed class is often a candidate Complex Type. But C# has no concept of composition—a class or property can’t be marked as a composition. The only difference is the object identifier: a complex type has no individual identity (i.e. no AddressId defined on Address class) which make sense because when it comes to the database everything is going to be saved into one single table. How to implement a Complex Types with Code First Code First has a concept of Complex Type Discovery that works based on a set of Conventions. The convention is that if Code First discovers a class where a primary key cannot be inferred, and no primary key is registered through Data Annotations or the fluent API, then the type will be automatically registered as a complex type. Complex type detection also requires that the type does not have properties that reference entity types (i.e. all the properties must be scalar types) and is not referenced from a collection property on another type. Here is the implementation: public class User{    public int UserId { get; set; }    public string FirstName { get; set; }    public string LastName { get; set; }    public string Username { get; set; }    public Address Address { get; set; }} public class Address {     public string Street { get; set; }     public string City { get; set; }            public string PostalCode { get; set; }        }public class EntityMappingContext : DbContext {     public DbSet<User> Users { get; set; }        } With code first, this is all of the code we need to write to create a complex type, we do not need to configure any additional database schema mapping information through Data Annotations or the fluent API. Database SchemaThe mapping result for this object model is as follows: Limitations of this mappingThere are two important limitations to classes mapped as Complex Types: Shared references is not possible: The Address Complex Type doesn’t have its own database identity (primary key) and so can’t be referred to by any object other than the containing instance of User (e.g. a Shipping class that also needs to reference the same User Address). No elegant way to represent a null reference There is no elegant way to represent a null reference to an Address. When reading from database, EF Code First always initialize Address object even if values in all mapped columns of the complex type are null. This means that if you store a complex type object with all null property values, EF Code First returns a initialized complex type when the owning entity object is retrieved from the database. SummaryIn this post we learned about fine-grained domain models which complex type is just one example of it. Fine-grained is fully supported by EF Code First and is known as the most important requirement for a rich domain model. Complex type is usually the simplest way to represent one-to-one relationships and because the lifecycle is almost always dependent in such a case, it’s either an aggregation or a composition in UML. In the next posts we will revisit the same domain model and will learn about other ways to map a one-to-one association that does not have the limitations of the complex types. References ADO.NET team blog Mapping Objects to Relational Databases Java Persistence with Hibernate

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• Taking Object Oriented development to the next level

  - by Songo

  Can you mention some advanced OO topics or concepts that one should be aware of? I have been a developer for 2 years now and currently aiming for a certain company that requires a web developer with a minimum experience of 3 years. I imagine the interview will have the basic object oriented topics like (Abstraction, Polymorphism, Inheritance, Design patterns, UML, Databases and ORMs, SOLID principles, DRY principle, ...etc) I have these topics covered, but what I'm looking forward to is bringing up topics such as Efferent Coupling, Afferent Coupling, Instability, The law of Demeter, ...etc. Till few days ago I never knew such concepts existed (maybe because I'm a communication engineer basically not a CS graduate.) Can you please recommend some more advanced topics concerning object oriented programming?

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• Help to translate SQL query to Relational Algebra

  - by Mestika

  Hi everyone, I'm having some difficulties with translating some queries to Relational Algebra. I've a great book about Database Design and here is a chapter about Relational Algebra but I still seem to have some trouble creating the right one: Thoes queries I've most difficuelt with is these: SELECT COUNT( cs.student_id ) AS counter FROM course c, course_student cs WHERE c.id = cs.course_id AND c.course_name = 'Introduction to Database Design' SELECT COUNT( cs.student_id ) FROM Course c INNER JOIN course_student cs ON c.id = cs.course_id WHERE c.course_name = 'Introduction to Database Design' and SELECT COUNT( * ) FROM student JOIN grade ON student.f_name = "Andreas" AND student.l_name = "Pedersen" AND student.id = grade.student_id I know the notation can be a bit hard to paste into HTML forum, but maybe just use some common name or the Greek name. Thanks in advance Mestika

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• relational data from xml

  - by Beta033

  Our problem is this, we have a relational database to store objects in tables. As any relational database could, several of these tables have multiple foreign keys pointing to other tables (all pretty normal stuff) We've been trying to identify a solution to allow export of this relational data, ideally, only 1 of the objects in the model, to some sort of file (xml, text, ??). So it wouldn't be simple enough to just export 1 table as data stored in other tables would contribute to the complete model of the object. Something like the following picture: Toward this, i've written a routine to export the structure by following the foreign key paths which exports something similar to the following. <Tables> <TableA PK="1", val1, val2, val3> <TableC PK="1", FK_A="1", Val1, val2, val3> <TableC PK="2", FK_A="1", val1, val2, val3> <TableB PK="1", FK_A="1", FK_C="1", val1, val2, val3> <TableB PK="2", FK_A="1", FK_C="2", val1, val2, val3> <TableD PK="1", FK_B="1", FK_C="1", val1> <TableD PK="2", FK_B="2", FK_C="1", val1> </Tables> However, given this structure, it cannot be placed into a heirarchial format (ie D2 is a child of C1 and B2; and B2 is a child of C2) Which in turn, makes my life very difficult when trying to identify a methodology to reimport (and reKey) these objects. Has anybody done anything like this? how do you do it? are there tools or documentation on how this is best accomplished? Thanks for your help.

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• How to use the client object model with SharePoint2010

  - by ybbest

  In SharePoint2010, you can use client object model to communicate with SharePoint server. Today, I’d like to show you how to achieve this by using the c# console application. You can download the solution here. 1. Create a Console application in visual studio and add the following references to the project. 2. Insert your code as below ClientContext context = new ClientContext("http://demo2010a"); Web currentWeb = context.Web; context.Load(currentWeb, web =&gt; web.Title); context.ExecuteQuery(); Console.WriteLine(currentWeb.Title); Console.ReadLine(); 3. Run your code then you will get the web title displayed as shown below Note: If you got the following errors, you need to change your target framework from .Net Framework 4 client profile to .Net Framework 4 as shown below: Change from TO

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• Object behaviour or separate class?

  - by Andrew Stephens

  When it comes to OO database access you see two common approaches - the first is to provide a class (say "Customer") with methods such as Retrieve(), Update(), Delete(), etc. The other is to keep the Customer class fairly lightweight (essentially just properties) and perform the database access elsewhere, e.g. using a repository. This choice of approaches doesn't just apply to database access, it can crop up in many different OOD scenarios. So I was wondering if one way is preferable over the other (although I suspect the answer will be "it depends")! Another dev on our team argues that to be truly OO the class should be "self-contained", i.e. providing all the methods necessary to manipulate and interact with that object. I personally prefer the repository approach - I don't like bloating the Customer class with all that functionality, and I feel it results in cleaner code having it elsewhere, but I can't help thinking I'm seriously violating core OO concepts! And what about memory implications? If I retrieve thousands of Customer objects I'm assuming those with the data access methods will take up a lot more memory than the property-only objects?

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• How do I add shadow mapping?

  - by Jasper Creyf

  How do I add shadow mapping? I don't care if it uses GLSL it just has to work. I have been searching on stencil shadows and shadow mapping, all the examples given did nothing, if you don't understand that it means not even a single shadow is even being rendered. If you know how to add stencil shadows or shadow mapping, then please show some java code and if you're using GLSL then please show the code for them too.

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• Any enlightenment for understanding Object Oriented Programming? [closed]

  - by ????

  I studied computer science near the end of 1980s, and wasn't taught OOP that formally. With Pascal or C, when I understand the top-down design of functions, and the idea of black box, then everything just seem to make sense, as if there is a "oh I get it!" -- some kind of totally getting it and enlightenment feeling. But with OOP, all I know was the mechanics: the class, instance, method, inheritance, polymorphism, encapsulation. It was like, I knew all the "this is how it is", but never had the feeling of "I totally get it", the enlightened feeling. Would somebody be able to describe it, or point to a chapter in some book or paper which talks about OOP so that the reader can feel: "I totally get it!" on OOP?

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• How to deploy jBPM 3.2.2 console on Oracle 10g iAS

  - by Balint Pato

  Hi! Does anybody have experience regarding deployment of the jBPM Administration Console on Oracle 10g iAS? I successfully deployed it using an .ear, security mappings working, I can even login to the console, Hibernate finds the JNDI datasource but it cannot find the TransactionManager. I see no log, only the exception thrown in the jsf page: Can anybody help me? The hibernate.cfg.xml file now looks like this: <?xml version='1.0' encoding='utf-8'?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <!-- hibernate dialect --> <property name="hibernate.dialect">org.hibernate.dialect.Oracle9Dialect</property> <!-- JDBC connection properties (begin) === <property name="hibernate.connection.driver_class">org.hsqldb.jdbcDriver</property> <property name="hibernate.connection.url">jdbc:hsqldb:mem:jbpm</property> <property name="hibernate.connection.username">sa</property> <property name="hibernate.connection.password"></property> ==== JDBC connection properties (end) --> <property name="hibernate.cache.provider_class">org.hibernate.cache.HashtableCacheProvider</property> <!-- DataSource properties (begin) --> <property name="hibernate.connection.datasource">java:/JbpmDS</property> <!-- DataSource properties (end) --> <!-- JTA transaction properties (begin) --> <property name="hibernate.transaction.factory_class">org.hibernate.transaction.JTATransactionFactory</property> <!-- <property name="hibernate.transaction.manager_lookup_class">org.hibernate.transaction.JBossTransactionManagerLookup</property>--> <!-- JTA transaction properties (end) --> <!-- CMT transaction properties (begin) === <property name="hibernate.transaction.factory_class">org.hibernate.transaction.CMTTransactionFactory</property> <property name="hibernate.transaction.manager_lookup_class">org.hibernate.transaction.JBossTransactionManagerLookup</property> ==== CMT transaction properties (end) --> <!-- logging properties (begin) --> <property name="hibernate.show_sql">true</property> <property name="hibernate.format_sql">true</property> <property name="hibernate.use_sql_comments">true</property> <--==== logging properties (end) --> <!-- ############################################ --> <!-- # mapping files with external dependencies # --> <!-- ############################################ --> <!-- following mapping file has a dependendy on --> <!-- 'bsh-{version}.jar'. --> <!-- uncomment this if you don't have bsh on your --> <!-- classpath. you won't be able to use the --> <!-- script element in process definition files --> <mapping resource="org/jbpm/graph/action/Script.hbm.xml"/> <!-- following mapping files have a dependendy on --> <!-- 'jbpm-identity.jar', mapping files --> <!-- of the pluggable jbpm identity component. --> <!-- Uncomment the following 3 lines if you --> <!-- want to use the jBPM identity mgmgt --> <!-- component. --> <!-- identity mappings (begin) --> <mapping resource="org/jbpm/identity/User.hbm.xml"/> <mapping resource="org/jbpm/identity/Group.hbm.xml"/> <mapping resource="org/jbpm/identity/Membership.hbm.xml"/> <!-- identity mappings (end) --> <!-- following mapping files have a dependendy on --> <!-- the JCR API --> <!-- jcr mappings (begin) === <mapping resource="org/jbpm/context/exe/variableinstance/JcrNodeInstance.hbm.xml"/> ==== jcr mappings (end) --> <!-- ###################### --> <!-- # jbpm mapping files # --> <!-- ###################### --> <!-- hql queries and type defs --> <mapping resource="org/jbpm/db/hibernate.queries.hbm.xml" /> <!-- graph.action mapping files --> <mapping resource="org/jbpm/graph/action/MailAction.hbm.xml"/> <!-- graph.def mapping files --> <mapping resource="org/jbpm/graph/def/ProcessDefinition.hbm.xml"/> <mapping resource="org/jbpm/graph/def/Node.hbm.xml"/> <mapping resource="org/jbpm/graph/def/Transition.hbm.xml"/> <mapping resource="org/jbpm/graph/def/Event.hbm.xml"/> <mapping resource="org/jbpm/graph/def/Action.hbm.xml"/> <mapping resource="org/jbpm/graph/def/SuperState.hbm.xml"/> <mapping resource="org/jbpm/graph/def/ExceptionHandler.hbm.xml"/> <mapping resource="org/jbpm/instantiation/Delegation.hbm.xml"/> <!-- graph.node mapping files --> <mapping resource="org/jbpm/graph/node/StartState.hbm.xml"/> <mapping resource="org/jbpm/graph/node/EndState.hbm.xml"/> <mapping resource="org/jbpm/graph/node/ProcessState.hbm.xml"/> <mapping resource="org/jbpm/graph/node/Decision.hbm.xml"/> <mapping resource="org/jbpm/graph/node/Fork.hbm.xml"/> <mapping resource="org/jbpm/graph/node/Join.hbm.xml"/> <mapping resource="org/jbpm/graph/node/MailNode.hbm.xml"/> <mapping resource="org/jbpm/graph/node/State.hbm.xml"/> <mapping resource="org/jbpm/graph/node/TaskNode.hbm.xml"/> <!-- context.def mapping files --> <mapping resource="org/jbpm/context/def/ContextDefinition.hbm.xml"/> <mapping resource="org/jbpm/context/def/VariableAccess.hbm.xml"/> <!-- taskmgmt.def mapping files --> <mapping resource="org/jbpm/taskmgmt/def/TaskMgmtDefinition.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/def/Swimlane.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/def/Task.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/def/TaskController.hbm.xml"/> <!-- module.def mapping files --> <mapping resource="org/jbpm/module/def/ModuleDefinition.hbm.xml"/> <!-- bytes mapping files --> <mapping resource="org/jbpm/bytes/ByteArray.hbm.xml"/> <!-- file.def mapping files --> <mapping resource="org/jbpm/file/def/FileDefinition.hbm.xml"/> <!-- scheduler.def mapping files --> <mapping resource="org/jbpm/scheduler/def/CreateTimerAction.hbm.xml"/> <mapping resource="org/jbpm/scheduler/def/CancelTimerAction.hbm.xml"/> <!-- graph.exe mapping files --> <mapping resource="org/jbpm/graph/exe/Comment.hbm.xml"/> <mapping resource="org/jbpm/graph/exe/ProcessInstance.hbm.xml"/> <mapping resource="org/jbpm/graph/exe/Token.hbm.xml"/> <mapping resource="org/jbpm/graph/exe/RuntimeAction.hbm.xml"/> <!-- module.exe mapping files --> <mapping resource="org/jbpm/module/exe/ModuleInstance.hbm.xml"/> <!-- context.exe mapping files --> <mapping resource="org/jbpm/context/exe/ContextInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/TokenVariableMap.hbm.xml"/> <mapping resource="org/jbpm/context/exe/VariableInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/variableinstance/ByteArrayInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/variableinstance/DateInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/variableinstance/DoubleInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/variableinstance/HibernateLongInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/variableinstance/HibernateStringInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/variableinstance/LongInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/variableinstance/NullInstance.hbm.xml"/> <mapping resource="org/jbpm/context/exe/variableinstance/StringInstance.hbm.xml"/> <!-- job mapping files --> <mapping resource="org/jbpm/job/Job.hbm.xml"/> <mapping resource="org/jbpm/job/Timer.hbm.xml"/> <mapping resource="org/jbpm/job/ExecuteNodeJob.hbm.xml"/> <mapping resource="org/jbpm/job/ExecuteActionJob.hbm.xml"/> <!-- taskmgmt.exe mapping files --> <mapping resource="org/jbpm/taskmgmt/exe/TaskMgmtInstance.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/exe/TaskInstance.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/exe/PooledActor.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/exe/SwimlaneInstance.hbm.xml"/> <!-- logging mapping files --> <mapping resource="org/jbpm/logging/log/ProcessLog.hbm.xml"/> <mapping resource="org/jbpm/logging/log/MessageLog.hbm.xml"/> <mapping resource="org/jbpm/logging/log/CompositeLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/ActionLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/NodeLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/ProcessInstanceCreateLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/ProcessInstanceEndLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/ProcessStateLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/SignalLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/TokenCreateLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/TokenEndLog.hbm.xml"/> <mapping resource="org/jbpm/graph/log/TransitionLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/VariableLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/VariableCreateLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/VariableDeleteLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/VariableUpdateLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/variableinstance/ByteArrayUpdateLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/variableinstance/DateUpdateLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/variableinstance/DoubleUpdateLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/variableinstance/HibernateLongUpdateLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/variableinstance/HibernateStringUpdateLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/variableinstance/LongUpdateLog.hbm.xml"/> <mapping resource="org/jbpm/context/log/variableinstance/StringUpdateLog.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/log/TaskLog.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/log/TaskCreateLog.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/log/TaskAssignLog.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/log/TaskEndLog.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/log/SwimlaneLog.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/log/SwimlaneCreateLog.hbm.xml"/> <mapping resource="org/jbpm/taskmgmt/log/SwimlaneAssignLog.hbm.xml"/> </session-factory> </hibernate-configuration> ---- edit --- I have already tried the hibernate.transaction.manager_lookup_class to set to the JBoss version (org.hibernate.transaction.JBossTransactionManagerLookup) it did not work...well it's not that suprising...I'll try now: org.hibernate.transaction.OC4JTransactionManagerLookup I tried with CMT instead of JTA, but it didn't work also.

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• Synonym for "Many-to-Many" relationship (relational databases)

  - by Byron

  What's a synonym for a "many-to-many" relationship? I've finished writing an object-relational mapper but I'm still stumped as to what to name the function that adds that relation. addParent() and addChild() seemed quite logical for the many-to-one/one-to-many and addSuperclass() for one-to-one inheritance, but addManyToMany() would sound quite unintuitive to an object-oriented programmer. addSibling() or addCousin() doesn't really make sense either. Any suggestions? And before you dismiss this as a non-programming question, please remember that consistent naming schemes and encapsulation are pretty integral to programming :)

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• Nhibernate/Hibernate, lookup tables and object design

  - by Simon G

  Hi, I've got two tables. Invoice with columns CustomerID, InvoiceDate, Value, InvoiceTypeID (CustomerID and InvoiceDate make up a composite key) and InvoiceType with InvoiceTypeID and InvoiceTypeName columns. I know I can create my objects like: public class Invoice { public virtual int CustomerID { get; set; } public virtual DateTime InvoiceDate { get; set; } public virtual decimal Value { get; set; } public virtual InvoiceType InvoiceType { get; set; } } public class InvoiceType { public virtual InvoiceTypeID { get; set; } public virtual InvoiceTypeName { get; set; } } So the generated sql would look something like: SELECT CustomerID, InvoiceDate, Value, InvoiceTypeID FROM Invoice WHERE CustomerID = x AND InvoiceDate = y SELECT InvoiceTypeID, InvoiceTypeName FROM InvoiceType WHERE InvoiceTypeID = z But rather that having two select queries executed to retrieve the data I would rather have one. I would also like to avoid using child object for simple lookup lists. So my object would look something like: public class Invoice { public virtual int CustomerID { get; set; } public virtual DateTime InvoiceDate { get; set; } public virtual decimal Value { get; set; } public virtual InvoiceTypeID { get; set; } public virtual InvoiceTypeName { get; set; } } And my sql would look something like: SELECT CustomerID, InvoiceDate, Value, InvoiceTypeID FROM Invoice INNER JOIN InvoiceType ON Invoice.InvoiceTypeID = InvoiceType.InvoiceTypeID WHERE CustomerID = x AND InvoiceDate = y My question is how do I create the mapping for this? I've tried using join but this tried to join using CustomerID and InvoiceDate, am I missing something obvious? Thanks

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