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• Many to many table design question

  - by user169867

  Originally I had 2 tables in my DB, [Property] and [Employee]. Each employee can have 1 "Home Property" so the employee table has a HomePropertyID FK field to Property. Later I needed to model the situation where despite having only 1 "Home Property" the employee did work at or cover for multiple properties. So I created an [Employee2Property] table that has EmployeeID and PropertyID FK fields to model this many 2 many relationship. Now I find that I need to create other many-to-many relationships between employees and properties. For example if there are multiple employees that are managers for a property or multiple employees that perform maintenance work at a property, etc. My questions are: 1) Should I create seperate many-to-many tables for each of these situations or should I just create 1 more table like [PropertyAssociatonType] that lists the types of associations an emploee can have with a property and just add a FK field to [Employee2Property] such a PropertyAssociationTypeID that explains what the association is? I'm curious about the pros/cons or if there's another better way. 2) Am I stupid and going about this all worng? Thanks for any suggestions :)

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• Using collections/containers/catalogs in Domain Models

  - by devoured elysium

  Let's say I want to model a cinema. The cinema will have a couple of rooms(for example, 7), where the movies are being played. I wonder how should I design the domain model for this scenario. Should the Cinema class concept concept have a direct association with the 7 rooms? Should the Cinema class concept have an association with a catalog of the 7 rooms? Why? I am having some trouble understanding why in some places I see the first case and in some others I see something like the second case. If instead of rooms, I wanted to depict the relationship between Cinema and: Tickets to sell (today). Tickets already sold (today) Customers in the Cinema database The set of hours at which there are movies playing in a given room in the cinema. The set of places you can sit at in a room in the cinema. Should I use catalogs, should I connect them directly to the Cinema concept with a multiplicity of * in the target? Thanks

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• Select multiple records from sql database table in a master-detail scenario

  - by Trex

  Hello, I have two tables in a master-detail relationship. The structure is more or less as follows: Master table: MasterID, DetailID, date, ... masterID1, detailID1, 2010/5/1, .... masterID2, detailID1, 2008/6/14, ... masterID3, detailID1, 2009/5/25, ... masterID4, detailID2, 2008/7/24, ... masterID5, detailID2, 2010/4/1, ... masterID6, detailID4, 2008/9/16, ... Details table: DetailID, ... detailID1, ... detailID2, ... detailID3, ... detailID4, ... I need to get all the records from the details table plus the LAST record from the master table (last by the date in the master table). Like this: detailID1, masterID1, 2010/5/1, .... detailID2, masterID5, 2010/4/1, ... detailID3, null, null, ... detailID4, masterID6, 2008/9/16, ... I have no idea how to do this. Can anybody help me? Thanks a lot. Jan

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• JDO, GAE: Load object group by child's key

  - by tiex

  I have owned one-to-many relationship between two objects: @PersistenceCapable(identityType = IdentityType.APPLICATION) public class AccessInfo { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private com.google.appengine.api.datastore.Key keyInternal; ... @Persistent private PollInfo currentState; public AccessInfo(){} public AccessInfo(String key, String voter, PollInfo currentState) { this.voter = voter; this.currentState = currentState; setKey(key); // this key is unique in whole systme } public void setKey(String key) { this.keyInternal = KeyFactory.createKey( AccessInfo.class.getSimpleName(), key); } public String getKey() { return this.keyInternal.getName(); } and @PersistenceCapable(identityType = IdentityType.APPLICATION) public class PollInfo { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key key; @Persistent(mappedBy = "currentState") private List<AccessInfo> accesses; ... I created an instance of class PollInfo and make it persistence. It is ok. But then I want to load this group by AccessInfo key, and I am getting exception NucleusObjectNotFoundException. Is it possible to load a group by child's key?

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• Using fields from an association (has_many) model with formtastic in rails

  - by pduersteler

  I searched and tried a lot, but I can't accomplish it as I want.. so here's my problem. class Moving < ActiveRecord::Base has_many :movingresources, :dependent => :destroy has_many :resources, :through => :movingresources end class Movingresource < ActiveRecord::Base belongs_to :moving belongs_to :resource end class Resource < ActiveRecord::Base has_many :movingresources has_many :movings, :through => :movingresources end Movingresources contains additional fields, like "quantity". We're working on the views for 'bill'. Thanks to formtastic to simplify the whole relationship thing by just writing <%= form.input :workers, :as => :check_boxes %> and i get a real nice checkbox list. But what I haven't found out so far is: How can i use the additional fields from 'movingresource', next or under each checkbox my desired fields from that model? I saw different approaches, mainly with manually looping through an array of objects and creating the appropriate forms, using :for in a form.inputs part, or not. But none of those solutions were clean (e.g. worked for the edit view but not for new because the required objects were not built or generated and generating them caused a mess). I want to know your solutions for this! :-)

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• Speeding up inner-joins and subqueries while restricting row size and table membership

  - by hiffy

  I'm developing an rss feed reader that uses a bayesian filter to filter out boring blog posts. The Stream table is meant to act as a FIFO buffer from which the webapp will consume 'entries'. I use it to store the temporary relationship between entries, users and bayesian filter classifications. After a user marks an entry as read, it will be added to the metadata table (so that a user isn't presented with material they have already read), and deleted from the stream table. Every three minutes, a background process will repopulate the Stream table with new entries (i.e. whenever the daemon adds new entries after the checks the rss feeds for updates). Problem: The query I came up with is hella slow. More importantly, the Stream table only needs to hold one hundred unread entries at a time; it'll reduce duplication, make processing faster and give me some flexibility with how I display the entries. The query (takes about 9 seconds on 3600 items with no indexes): insert into stream(entry_id, user_id) select entries.id, subscriptions_users.user_id from entries inner join subscriptions_users on subscriptions_users.subscription_id = entries.subscription_id where subscriptions_users.user_id = 1 and entries.id not in (select entry_id from metadata where metadata.user_id = 1) and entries.id not in (select entry_id from stream where user_id = 1); The query explained: insert into stream all of the entries from a user's subscription list (subscriptions_users) that the user has not read (i.e. do not exist in metadata) and which do not already exist in the stream. Attempted solution: adding limit 100 to the end speeds up the query considerably, but upon repeated executions will keep on adding a different set of 100 entries that do not already exist in the table (with each successful query taking longer and longer). This is close but not quite what I wanted to do. Does anyone have any advice (nosql?) or know a more efficient way of composing the query?

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• How do I left join tables in unidirectional many-to-one in Hibernate?

  - by jbarz

  I'm piggy-backing off of http://stackoverflow.com/questions/2368195/how-to-join-tables-in-unidirectional-many-to-one-condition. If you have two classes: class A { @Id public Long id; } class B { @Id public Long id; @ManyToOne @JoinColumn(name = "parent_id", referencedColumnName = "id") public A parent; } B - A is a many to one relationship. I understand that I could add a Collection of Bs to A however I do not want that association. So my actual question is, Is there an HQL or Criteria way of creating the SQL query: select * from A left join B on (b.parent_id = a.id) This will retrieve all A records with a Cartesian product of each B record that references A and will include A records that have no B referencing them. If you use: from A a, B b where b.a = a then it is an inner join and you do not receive the A records that do not have a B referencing them. I have not found a good way of doing this without two queries so anything less than that would be great. Thanks.

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• Complicated SQL query

  - by Yandawl

  Please bare with me this is difficult to explain xD http://img90.imageshack.us/i/croppercapture1.png/ This is based on an undergraduate degree course where a student takes many units (say 4 core units and 1 optional unit per year). tblAwardCoreUnits and tblAwardOptUnits store which units are optional and core for which award, hence the relationship to tblAward and tblStudentCoreUnits and tblStudentOptUnits store the particular instances of those units which a particular student is taking. Secondly, a unit can have multiple events (say a lecture and a unit) and each of those events has sessions in which a student can attend, hence tblEvents, tblSessions and tblAttendances. The query I am trying to produce is to get a list of all level one students, grouped by their award that lists the percentage of attendances in all the units in the current level. I've tried and tried with this and the following is the best I've managed to come up with so far... I'd REALLY appreciate any help you can give with this! SELECT tblStudents.enrolmentNo, tblStudents.forename, tblStudents.surname, tblAwards.title, (SELECT COUNT((tblAttendances.attended + tblAttendances.authorisedAbsence)) AS SumOfAttendances FROM tblAttendances INNER JOIN (tblStudents ON tblStudents.enrolmentNo = tblAttendances.enrolmentNo)) / FROM tblUnits, tblAwards INNER JOIN ((tblStudents INNER JOIN tblStudentOptUnit ON tblStudents.studentID = tblStudentOptUnit.studentID) INNER JOIN tblStudentCoreUnit ON tblStudents.studentID = tblStudentCoreUnit.studentID) ON tblAwards.awardID = tblStudents.awardID WHERE (((tblStudents.level)="1") AND ((tblStudents.status)="enrolled")) GROUP BY tblAwards.title ORDER BY tblStudents.forname;

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• NHibernate complex order query

  - by manu08

  Here's my simplified domain public class Notification { public Guid ID { get; set; } public string Name { get; set; } public IEnumerable<Location> Locations { get; set; } } public class Location { public Guid Id { get; set; } public string Name { get; set; } public decimal Longitude { get; set; } public decimal Latitude { get; set; } } Notifications and Locations have a many-to-many relationship (defined in table LocationsOnNotification). What I'd like to do is query for the nearest 10 Notifications from a given longitude and latitude. I've been trying to use ICriteria, but I'm not sure how to specify the ordering correctly: return Session.CreateCriteria<Notification>() .SetFirstResult(firstIndex) .SetMaxResults(maxResults) .AddOrder(Order.Asc( WHAT GOES HERE! )) .List<Notification>(); What I've been thinking of so far is adding a formula property to the Location mapping; something like this: <property name='Distance' formula='lots of geometry'/> But I'm not sure if that can take in parameters (since I'd need to pass in the user's location to calculate the distance), plus I'm not sure how to specify it in the Order.Asc clause given that it's a property on a many-to-many association class. Any ideas? Or perhaps I should take a different approach altogether. Thanks in advance!

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• How to handle management trying to interfere with the project (including architecture decision)

  - by Zwei Steinen

  I feel this is not a very good question to post on SO, but I need some advice from experienced developers... (I'm a second year developer) I guess this is a problem to many, many projects, but in our case, it is getting intense. There were so much interference from people that don't know a bit about software development, that our development came to an almost complete stop. We had to literary escape to another location to get any useful job done. Now we were happily producing results, but then I get a request for a "meeting" and it's them again. I have a friendly relationship with them, but I feel very daunted at the thought of talking about non-sense all over again. Should I be firm and tell them to shut up and wait for our results? Or should I be diplomatic and create an illusion they are making a positive contribution or something?? My current urge is to be unfriendly and murmur some stuff so they will give up or something. What would you do if you were in this situation?

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• Reducing the opacity on a div without reducing the opacity of the contents

  - by user352744

  Want to reduce the opacity of page contents container background without reducing the opacity of the contents. <div id="container"> <div id="page contents"> page contents goes here, like amazing articles and all that. </div> </div> Needs to be able to expand with the content, thus can't have a fixed height. Absolute positioning it underneath the content will mean there will be no relationship between the two divs and it wont expand with the contents, so I think this is a dead end, feel free to say otherwise. Can't use Jquery as could be too laggy and not instant. Other options preferred please. May have to use 'png' background images but were hoping not to as it is a template and needs to be able to change colour based on colour schemes. Could generate images on demand but not ideal. Oh and to top it off cant use CSS3 as wont work in IE! of course! Any suggestions?

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• Add child to existing parent record in entity framework.

  - by Shawn Mclean

  My relationship between the parent and child is that they are connected by an edge. It is similiar to a directed graph structure. DAL: public void SaveResource(Resource resource) { context.AddToResources(resource); //Should also add children. context.SaveChanges(); } public Resource GetResource(int resourceId) { var resource = (from r in context.Resources .Include("ToEdges").Include("FromEdges") where r.ResourceId == resourceId select r).SingleOrDefault(); return resource; } Service: public void AddChildResource(int parentResourceId, Resource childResource) { Resource parentResource = repository.GetResource(parentResourceId); ResourceEdge inEdge = new ResourceEdge(); inEdge.ToResource = childResource; parentResource.ToEdges.Add(inEdge); repository.SaveResource(parentResource); } Error: An object with the same key already exists in the ObjectStateManager. The existing object is in the Unchanged state. An object can only be added to the ObjectStateManager again if it is in the added state. Image: I have been told this is the sequence in submitting a child to an already existing parent: Get parent - Attach Child to parent - submit parent. That is the sequence I used. The code above is extracted from an ASP.NET MVC 2 application using the repository pattern.

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• How to update non-scalar entity properties in EF 4.0?

  - by Mike

  At first I was using this as an extension method to update my detached entities... Public Sub AttachUpdated(ByVal obj As ObjectContext, ByVal objectDetached As EntityObject) If objectDetached.EntityState = EntityState.Detached Then Dim original As Object = Nothing If obj.TryGetObjectByKey(objectDetached.EntityKey, original) Then obj.ApplyCurrentValues(objectDetached.EntityKey.EntitySetName, objectDetached) Else Throw New ObjectNotFoundException() End If End If End Sub Everything has been working great until I had to update non-scalar properties. Correct me if I am wrong but that is because "ApplyCurrentValues" only supports scalars. To get around this I was just saving the FK_ID field instead of the entity object relation. Now I am faced with a many to many relationship so its not that simple. I would like to do something like this... Dim Resource = RelatedResource.GetByID(item.Value) Condition.RelatedResources.Add(Resource) But when I call SaveChanges the added Resources aren't saved. I started to play around with self-tracking entities (not sure if they will help solve my prob) but it seems they cannot be serialized to ViewState and this is a requirement for me. I guess one solution would be to add the xRef table as an entity and add the fks myself but I would rather it just work how I expect it too. I am open to any suggestions on how to either save my many to many relationships or serialize self-tracking entities (if self-trackingwould even solve my problem). Thanks!

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• How to model parent to child pair in MySQL (SQL)

  - by mikeschuld

  I have a data model that includes element types Stage, Actor, and Form. Logically, Stages can be assigned pairs of ( Form <--- Actor ) which can be duplicated many times (i.e. same person and same form added to the same stage at a later date/time). Right now I am modeling this with these tables: Stage Form Actor Form_Actor _______________ |Id | |FormId | --> Id in Form |ActorId | --> Id in Actor Stage_FormActor __________________ |Id | |StageId | --> Id in Stage |FormActorId | --> Id in Form_Actor I am using CodeSmith to generate the data layer for this setup and none of the templates really know how to handle this type of relationship correctly when generating classes. Ideally, the ORM would have Stage.FormActors where FormActor would be the pair Form, Actor. Is this the correct way to model these relationships. I have tried using all three Ids in one table as well Stage_Form_Actor ______________ |Id | |StageId | --> Id in Stage |FormId | --> Id in Form |ActorId | --> Id in Actor This doesn't really get generated very well either. Ideas?

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• How does a client find the port number of a server?

  - by Jonathan

  Hello all, I am currently learning about basic networking in java. I have been playing around with the server and client relationship between two of my computers. However, I cannot figure out how distributed programs (say, a videogame), can not only find the 'host' computer, but also the port number on which the server is running in order to create a Socket between the two computers. The only way I really see to create a Socket is with an already known IP Address, and with a known port number. How do you search a LAN network for another computer (host) searching for clients? How do you determine what port the server is located on without 'pinging' all available ports for a response (which, I understand, is bad form... Something about 'server attack'...)? In such a situation as a video game, there can be any number of computers on the same network, and any number of them might be attempting to host, or otherwise running the application. Any other important information, or perhaps reference to a more detailed tutorial than the one I am using, regarding making connections on so very little information on the client side would be appreciated. Many thanks, Jonathan

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• Working with extra fields in an Inline form - save_model, save_formset, can't make sense of the diff

  - by magicrebirth

  Suppose I am in the usual situation where there're extra fields in the many2many relationship: class Person(models.Model): name = models.CharField(max_length=128) class Group(models.Model): name = models.CharField(max_length=128) members = models.ManyToManyField(Person, through='Membership') class Membership(models.Model): person = models.ForeignKey(Person) group = models.ForeignKey(Group) date_joined = models.DateField() invite_reason = models.CharField(max_length=64) # other models which are unrelated to the ones above.. class Trip(models.Model): placeVisited = models.ForeignKey(Place) visitor = models.ForeignKey(Person) pleasuretrip = models.Boolean() class Place(models.Model): name = models.CharField(max_length=128) I want to add some extra fields in the Membership form that gets displayed through the Inline. These fields basically are a shortcut to the instantiation of another model (Trip). Trip can have its own admin views, but these shortcuts are needed because when my project partners are entering 'Membership' data in the system they happen to have also the 'Trip' information handy (and also because some of the info in Membership can just be copied over to Trip etc. etc.). So all I want to have is two extra fields in the Membership Inline - placeVisited and pleasuretrip - which together with the Person instance will let me instantiate the Trip model in the background... I found out I can easily add extra fields to the inline view by defining my own form. But once the data have been entered, how and when to reference to them in order to perform the save operations I need to do? class MyForm(forms.ModelForm): place = forms.ModelChoiceField(required=False, queryset=Place.objects.all(), label="place",) pleasuretrip = forms.BooleanField(required=False, label="...") class MembershipInline(admin.TabularInline): model = Membership form = MyForm def save_model(self, request, obj, form, change): place = form.place pleasuretrip = form.pleasuretrip person = form.person .... # now I can create Trip instances with those data .... obj.save() class GroupAdmin(admin.ModelAdmin): model = Group .... inlines = (MembershipInline,) This doesn't seem to work... I'm also a bit puzzled by the save_formset method... maybe is that the one I should be using? Many thanks in advance for the help!!!!

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• Why does Microsoft advise against readonly fields with mutable values?

  - by Weeble

  In the Design Guidelines for Developing Class Libraries, Microsoft say: Do not assign instances of mutable types to read-only fields. The objects created using a mutable type can be modified after they are created. For example, arrays and most collections are mutable types while Int32, Uri, and String are immutable types. For fields that hold a mutable reference type, the read-only modifier prevents the field value from being overwritten but does not protect the mutable type from modification. This simply restates the behaviour of readonly without explaining why it's bad to use readonly. The implication appears to be that many people do not understand what "readonly" does and will wrongly expect readonly fields to be deeply immutable. In effect it advises using "readonly" as code documentation indicating deep immutability - despite the fact that the compiler has no way to enforce this - and disallows its use for its normal function: to ensure that the value of the field doesn't change after the object has been constructed. I feel uneasy with this recommendation to use "readonly" to indicate something other than its normal meaning understood by the compiler. I feel that it encourages people to misunderstand the meaning of "readonly", and furthermore to expect it to mean something that the author of the code might not intend. I feel that it precludes using it in places it could be useful - e.g. to show that some relationship between two mutable objects remains unchanged for the lifetime of one of those objects. The notion of assuming that readers do not understand the meaning of "readonly" also appears to be in contradiction to other advice from Microsoft, such as FxCop's "Do not initialize unnecessarily" rule, which assumes readers of your code to be experts in the language and should know that (for example) bool fields are automatically initialised to false, and stops you from providing the redundancy that shows "yes, this has been consciously set to false; I didn't just forget to initialize it". So, first and foremost, why do Microsoft advise against use of readonly for references to mutable types? I'd also be interested to know: Do you follow this Design Guideline in all your code? What do you expect when you see "readonly" in a piece of code you didn't write?

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• SCD2 + Merge Statement + MSSQL

  - by Nev_Rahd

  I am trying work out with MERGE statment to Insert / Update Dimension Table of Type SCD2 My source is a Table var to Merge with Dimension table. My Merget statement is throwing an error as: The target table 'DM.DATA_ERROR.ERROR_DIMENSION' of the INSERT statement cannot be on either side of a (primary key, foreign key) relationship when the FROM clause contains a nested INSERT, UPDATE, DELETE, or MERGE statement. Found reference constraint 'FK_ERROR_DIMENSION_to_AUDIT_CreatedBy'. My Merge Statement: DECLARE @DATAERROROBJECT AS [ERROR_DIMENSION] INSERT INTO DM.DATA_ERROR.ERROR_DIMENSION SELECT ERROR_CODE, DATA_STREAM_ID, [ERROR_SEVERITY], DATA_QUALITY_RATING, ERROR_LONG_DESCRIPTION, ERROR_DESCRIPTION, VALIDATION_RULE, ERROR_TYPE, ERROR_CLASS, VALID_FROM, VALID_TO, CURR_FLAG, CREATED_BY_AUDIT_SK, UPDATED_BY_AUDIT_SK FROM (MERGE DM.DATA_ERROR.ERROR_DIMENSION ED USING @DATAERROROBJECT OBJ ON(ED.ERROR_CODE = OBJ.ERROR_CODE AND ED.DATA_STREAM_ID = OBJ.DATA_STREAM_ID) WHEN NOT MATCHED THEN INSERT VALUES( OBJ.ERROR_CODE ,OBJ.DATA_STREAM_ID ,OBJ.[ERROR_SEVERITY] ,OBJ.DATA_QUALITY_RATING ,OBJ.ERROR_LONG_DESCRIPTION ,OBJ.ERROR_DESCRIPTION ,OBJ.VALIDATION_RULE ,OBJ.ERROR_TYPE ,OBJ.ERROR_CLASS ,GETDATE() ,'9999-12-13' ,'Y' ,1 ,1 ) WHEN MATCHED AND ED.CURR_FLAG = 'Y' AND ( ED.[ERROR_SEVERITY] <> OBJ.[ERROR_SEVERITY] OR ED.[DATA_QUALITY_RATING] <> OBJ.[DATA_QUALITY_RATING] OR ED.[ERROR_LONG_DESCRIPTION] <> OBJ.[ERROR_LONG_DESCRIPTION] OR ED.[ERROR_DESCRIPTION] <> OBJ.[ERROR_DESCRIPTION] OR ED.[VALIDATION_RULE] <> OBJ.[VALIDATION_RULE] OR ED.[ERROR_TYPE] <> OBJ.[ERROR_TYPE] OR ED.[ERROR_CLASS] <> OBJ.[ERROR_CLASS] ) THEN UPDATE SET ED.CURR_FLAG = 'N', ED.VALID_TO = GETDATE() OUTPUT $ACTION ACTION_OUT, OBJ.ERROR_CODE ERROR_CODE, OBJ.DATA_STREAM_ID DATA_STREAM_ID, OBJ.[ERROR_SEVERITY] [ERROR_SEVERITY], OBJ.DATA_QUALITY_RATING DATA_QUALITY_RATING, OBJ.ERROR_LONG_DESCRIPTION ERROR_LONG_DESCRIPTION, OBJ.ERROR_DESCRIPTION ERROR_DESCRIPTION, OBJ.VALIDATION_RULE VALIDATION_RULE, OBJ.ERROR_TYPE ERROR_TYPE, OBJ.ERROR_CLASS ERROR_CLASS, GETDATE() VALID_FROM, '9999-12-31' VALID_TO, 'Y' CURR_FLAG, 555 CREATED_BY_AUDIT_SK, 555 UPDATED_BY_AUDIT_SK ) AS MERGE_OUT WHERE MERGE_OUT.ACTION_OUT = 'UPDATE'; What am i doing wrong ?

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• The rules to connect a web service trough the SSL and Certificates

  - by blgnklc

  There is a web service running on tomcat on a server. It is built on Java Servlet. It is listening others to call itself on a SSL enabled http port. so its web service adreess looks like: https://172.29.12.12/axis/services/XYZClient?wsdl On the other hand I want to connect the web service above from a windows application which is built on .NET frame work. Finally, when I want to connect the web service from my computer; I get some specific erros; Firstly I get; Proxy authentication error; then I added some new line to my code; Dim cr As System.Net.NetworkCredential = New System.Net.NetworkCredential("xname", "xsurname", "xdomainname") Dim myProxy As New WebProxy("http://mar.xxxyyy.com", True) myProxy.Credentials = cr Secondly, after this modifications It says that bad request. I did not get over this error. Moreover I did try to connect the web server on the same computer. I copied my executable program to the computer where the web service runs. The error was like; The underlying connection was closed: Could not establish trust relationship for SSL/TLS secure channel PS: When I try to connect to web service by using Internet Explorer; I see firstly some warnings about accepting an unknown certificate and I click take me to web service an I get there clearly. I want to know what are the basic elements to connect a web service, could you please tell me the requirements that I have to use on my windows project. regards bk

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• EF 6 Code First Many to many With Payload and self referencing many to many

  - by lesley86

  I Have the problem where i have a many to many relationship and on one of the tables there will be a self referencing many to many. So basically a school have zero or many groups and many groups can have 0 or many schools. The groups table will contain a parent child many to many with itself because a group can be a child of another group or it can have no children and that child can have a child, one child can also have many parents or a entity can have no parents. I created a mapping table with Payload to solvethe first many to many problem. code snippet public class School { public virtual ICollection<SchoolGroupMap> SchoolGroupMaps } public class SchoolGroup { public virtual ICollection<SchoolGroupMap> SchoolGroupMaps } public class SchoolGroupMap { public virtual School School public virtual SchoolGroup SchoolGroup } i Then tried modifying the code the following way for the the self referencing many to many public class SchoolGroup { public virtual ICollection<SchoolGroupMap> SchoolGroupMaps public virtual ICollection<SchoolGroup> Parents public virtual ICollection<SchoolGroup> Children } I changed the context with has many and an auto mapping table (forgive me i have been trying so many things today i do not have the exact code). I received an error the properties on the classes must match. Can anyone help please. I want to do create navigation properties on the self referencing many to many. Also a seed example would be appreciated regards

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• How can I make this LinqToSQL query work? (SqlExecption)

  - by kversch

  The following code gives me an SqlException: OO theCourse = subject.Course; var students = dc.studentsCourses.Where(x = x.course == theCourse).Select(x = x.student); "Invalid object name 'dbo.studentsCourses'." I tried the following code instead but I also get an Exception. My original question was asked on Aardvark and can be read bellow: var allStudents = from s in dc.students select s; List thestudents = new List(); foreach (student s in allStudents) { if (s.courses.Contains(theCourse)) { thestudents.Add(s); } } I did a right click, "run custom tool" on my dbml and checked my names of my tables and entities. The project compiles but I get an Exception at runtime on this line: "if (s.courses.Contains(theCourse))" Any ideas? Original question on Aardvark: How do I do a LinqToSQL query that gives me this: I want to select all students that attended a certain lesson. The lesson is from a certain course. So select the course the lesson is from. Now select all the students that are following that course. There is a many-to-many relationship between the students and the courses table in my DB. I already extended my LINQ entities to be able to select student.Courses and course.Students using this method: http://www.codeproject.com/KB/linq/linq-to-sql-many-to-many.aspx

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• JPA concatenating table names for parent/child @OneToMany

  - by Robert

  We are trying to use a basic @OneToMany relationship: @Entity @Table(name = "PARENT_MESSAGE") public class ParentMessage { @Id @Column(name = "PARENT_ID") @GeneratedValue(strategy = GenerationType.IDENTITY) private Integer parentId; @OneToMany(fetch=FetchType.LAZY) private List childMessages; public List getChildMessages() { return this.childMessages; } ... } @Entity @Table(name = "CHILD_MSG_USER_MAP") public class ChildMessage { @Id @Column(name = "CHILD_ID") @GeneratedValue(strategy = GenerationType.IDENTITY) private Integer childId; @ManyToOne(optional=false,targetEntity=ParentMessage.class,cascade={CascadeType.REFRESH}, fetch=FetchType.LAZY) private ParentMessage parentMsg; public ParentMessage getParentMsg() { return parentMsg; } ... } ChildMessage child = new ChildMessage(); em.getTransaction().begin(); ParentMessage parentMessage = (ParentMessage) em.find(ParentMessage.class, parentId); child.setParentMsg(parentMessage); List list = parentMessage.getChildMessages(); if(list == null) list = new ArrayList(); list.add(child); em.getTransaction().commit(); We receive the following error. Why is OpenJPA concatenating the table names to APP.PARENT_MESSAGE_CHILD_MSG_USER_MAP? Of course that table doesn't exist.. the tables defined are APP.PARENT_MESSAGE and APP.CHILD_MSG_USER_MAP Caused by: org.apache.openjpa.lib.jdbc.ReportingSQLException: Table/View 'APP.PARENT_MESSAGE_CHILD_MSG_USER_MAP' does not exist. {SELECT t1.CHILD_ID, t1.PARENT_ID, t1.CREATED_TIME, t1.USER_ID FROM APP.PARENT_MESSAGE_CHILD_MSG_USER_MAP t0 INNER JOIN APP.CHILD_MSG_USER_MAP t1 ON t0.CHILDMESSAGES_CHILD_ID = t1.CHILD_ID WHERE t0.PARENTMESSAGE_PARENT_ID = ?} [code=30000, state=42X05]

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• ASP.NET MVC Patterns

  - by Sam Striano

  Hello, I am fairly new to MVC, but after playing with it (MVC 3/Razor), I am hooked. I have a few questions: 1) What is the best, or most widely used pattern to develop MVC apps in? Repository, DDD, UOW? 2) I am using the Entity Framework 4, so could some please explain to me or point me to a good source that will explain the Repository Pattern w/EF4? Doesn't EF4 take place as the business layer and the data access layer? Does the Repository Pattern even provide a benefit? 3) Also, one last question, could someone explain the whole relationship between the Controller, the Model and the View? I get the basics, but maybe a little more in depth of the correct way to use it. View Models - Say I have a view that displays customer info, and one that edits it, should I have a view model and an edit model, or can the be passed around? 4) Examples?? Thanks for the help up front, $("Sam") ** EDIT ** Am I on the right track here: Public Class HomeController Inherits System.Web.Mvc.Controller Function Index(ByVal id As Integer) As ActionResult Return View(New HomeModel) End Function <HttpPost()> _ Function Index(ByVal Model As HomeModel) As ActionResult Return View(Model) End Function End Class Public Class HomeModel Private _Repository As IRepository(Of Customer) Public Property Customer As Customer Public Sub New() End Sub Public Sub New(ByVal ID As Integer) _Repository = New CustomerRepository Customer = _Repository.GetByID(ID) End Sub End Class Public Interface IRepository(Of T) Function GetByID(ByVal ID As Integer) As T Sub Add(ByVal Entity As T) Sub Delete(ByVal Entity As T) End Interface Public Class CustomerRepository Implements IRepository(Of Customer) Public Sub Add(ByVal Entity As Customer) Implements IRepository(Of Customer).Add End Sub Public Sub Delete(ByVal Entity As Customer) Implements IRepository(Of Customer).Delete End Sub Public Function GetByID(ByVal ID As Integer) As Customer Implements IRepository(Of Customer).GetByID Return New Customer With {.ID = ID, .FirstName = "Sam", .LastName = "Striano"} End Function End Class Public Class Customer Public Property ID As Integer Public Property FirstName As String Public Property LastName As String End Class

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• Is it possible to order by a composite key with JPA and CriteriaBuilder

  - by Kjir

  I would like to create a query using the JPA CriteriaBuilder and I would like to add an ORDER BY clause. This is my entity: @Entity @Table(name = "brands") public class Brand implements Serializable { public enum OwnModeType { OWNER, LICENCED } @EmbeddedId private IdBrand id; private String code; //bunch of other properties } Embedded class is: @Embeddable public class IdBrand implements Serializable { @ManyToOne private Edition edition; private String name; } And the way I am building my query is like this: CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Brand> q = cb.createQuery(Brand.class).distinct(true); Root<Brand> root = q.from(Brand.class); if (f != null) { f.addCriteria(cb, q, root); f.addOrder(cb, q, root, sortCol, ascending); } return em.createQuery(q).getResultList(); And here are the functions called: public void addCriteria(CriteriaBuilder cb, CriteriaQuery<?> q, Root<Brand> r) { } public void addOrder(CriteriaBuilder cb, CriteriaQuery<?> q, Root<Brand> r, String sortCol, boolean ascending) { if (ascending) { q.orderBy(cb.asc(r.get(sortCol))); } else { q.orderBy(cb.desc(r.get(sortCol))); } } If I try to set sortCol to something like "id.edition.number" I get the following error: javax.ejb.EJBException: java.lang.IllegalArgumentException: Unable to resolve attribute [id.name] against path Any idea how I could accomplish that? I tried searching online, but I couldn't find a hint about this... Also would be great if I could do a similar ORDER BY when I have a @ManyToOne relationship (for instance, "id.edition.number")

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• Designing small comparable objects

  - by Thomas Ahle

  Intro Consider you have a list of key/value pairs: (0,a) (1,b) (2,c) You have a function, that inserts a new value between two current pairs, and you need to give it a key that keeps the order: (0,a) (0.5,z) (1,b) (2,c) Here the new key was chosen as the average between the average of keys of the bounding pairs. The problem is, that you list may have milions of inserts. If these inserts are all put close to each other, you may end up with keys such to 2^(-1000000), which are not easily storagable in any standard nor special number class. The problem How can you design a system for generating keys that: Gives the correct result (larger/smaller than) when compared to all the rest of the keys. Takes up only O(logn) memory (where n is the number of items in the list). My tries First I tried different number classes. Like fractions and even polynomium, but I could always find examples where the key size would grow linear with the number of inserts. Then I thought about saving pointers to a number of other keys, and saving the lower/greater than relationship, but that would always require at least O(sqrt) memory and time for comparison. Extra info: Ideally the algorithm shouldn't break when pairs are deleted from the list.

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