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  • EF4 generates invalid script

    - by Jaxidian
    When I right-click in a .EDMX file and click Generate Database From Model, the resulting script is obviously wrong because of the table names. What it generates is the following script. Note the table names in the DROP TABLE part versus the CREATE TABLE part. Why is this inconsistent? This is obviously not a reusable script. What I created was an Entity named "Address" and an Entity named "Company", etc (all singular). The EntitySet names are pluralized. The "Pluralize New Objects" boolean does not change this either. So what's the deal? For what it's worth, I originally generated the EDMX by pointing it to a database that had tables with non-pluralized names and now that I've made some changes, I want to go back the other way. I'd like to have the option to go back and forth as neither the db-first nor the model-first model is ideal in all scenarios, and I have the control to ensure that there will be no merging issues from multiple people going both ways at the same time. -- -------------------------------------------------- -- Dropping existing FOREIGN KEY constraints -- NOTE: if the constraint does not exist, an ignorable error will be reported. -- -------------------------------------------------- ALTER TABLE [Address] DROP CONSTRAINT [FK_Address_StateID-State_ID]; GO ALTER TABLE [Company] DROP CONSTRAINT [FK_Company_AddressID-Address_ID]; GO ALTER TABLE [Employee] DROP CONSTRAINT [FK_Employee_BossEmployeeID-Employee_ID]; GO ALTER TABLE [Employee] DROP CONSTRAINT [FK_Employee_CompanyID-Company_ID]; GO ALTER TABLE [Employee] DROP CONSTRAINT [FK_Employee_PersonID-Person_ID]; GO ALTER TABLE [Person] DROP CONSTRAINT [FK_Person_AddressID-Address_ID]; GO -- -------------------------------------------------- -- Dropping existing tables -- NOTE: if the table does not exist, an ignorable error will be reported. -- -------------------------------------------------- DROP TABLE [Address]; GO DROP TABLE [Company]; GO DROP TABLE [Employee]; GO DROP TABLE [Person]; GO DROP TABLE [State]; GO -- -------------------------------------------------- -- Creating all tables -- -------------------------------------------------- -- Creating table 'Addresses' CREATE TABLE [Addresses] ( [ID] int IDENTITY(1,1) NOT NULL, [StreetAddress] nvarchar(100) NOT NULL, [City] nvarchar(100) NOT NULL, [StateID] int NOT NULL, [Zip] nvarchar(10) NOT NULL ); GO -- Creating table 'Companies' CREATE TABLE [Companies] ( [ID] int IDENTITY(1,1) NOT NULL, [Name] nvarchar(100) NOT NULL, [AddressID] int NOT NULL ); GO -- Creating table 'People' CREATE TABLE [People] ( [ID] int IDENTITY(1,1) NOT NULL, [FirstName] nvarchar(100) NOT NULL, [LastName] nvarchar(100) NOT NULL, [AddressID] int NOT NULL ); GO -- Creating table 'States' CREATE TABLE [States] ( [ID] int IDENTITY(1,1) NOT NULL, [Name] nvarchar(100) NOT NULL, [Abbreviation] nvarchar(2) NOT NULL ); GO -- Creating table 'Employees' CREATE TABLE [Employees] ( [ID] int IDENTITY(1,1) NOT NULL, [PersonID] int NOT NULL, [CompanyID] int NOT NULL, [Position] nvarchar(100) NOT NULL, [BossEmployeeID] int NULL ); GO -- -------------------------------------------------- -- Creating all PRIMARY KEY constraints -- -------------------------------------------------- -- Creating primary key on [ID] in table 'Addresses' ALTER TABLE [Addresses] ADD CONSTRAINT [PK_Addresses] PRIMARY KEY ([ID] ); GO -- Creating primary key on [ID] in table 'Companies' ALTER TABLE [Companies] ADD CONSTRAINT [PK_Companies] PRIMARY KEY ([ID] ); GO -- Creating primary key on [ID] in table 'People' ALTER TABLE [People] ADD CONSTRAINT [PK_People] PRIMARY KEY ([ID] ); GO -- Creating primary key on [ID] in table 'States' ALTER TABLE [States] ADD CONSTRAINT [PK_States] PRIMARY KEY ([ID] ); GO -- Creating primary key on [ID] in table 'Employees' ALTER TABLE [Employees] ADD CONSTRAINT [PK_Employees] PRIMARY KEY ([ID] ); GO -- -------------------------------------------------- -- Creating all FOREIGN KEY constraints -- -------------------------------------------------- -- Creating foreign key on [StateID] in table 'Addresses' ALTER TABLE [Addresses] ADD CONSTRAINT [FK_Address_StateID_State_ID] FOREIGN KEY ([StateID]) REFERENCES [States] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Address_StateID_State_ID' CREATE INDEX [IX_FK_Address_StateID_State_ID] ON [Addresses] ([StateID]); GO -- Creating foreign key on [AddressID] in table 'Companies' ALTER TABLE [Companies] ADD CONSTRAINT [FK_Company_AddressID_Address_ID] FOREIGN KEY ([AddressID]) REFERENCES [Addresses] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Company_AddressID_Address_ID' CREATE INDEX [IX_FK_Company_AddressID_Address_ID] ON [Companies] ([AddressID]); GO -- Creating foreign key on [AddressID] in table 'People' ALTER TABLE [People] ADD CONSTRAINT [FK_Person_AddressID_Address_ID] FOREIGN KEY ([AddressID]) REFERENCES [Addresses] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Person_AddressID_Address_ID' CREATE INDEX [IX_FK_Person_AddressID_Address_ID] ON [People] ([AddressID]); GO -- Creating foreign key on [CompanyID] in table 'Employees' ALTER TABLE [Employees] ADD CONSTRAINT [FK_Employee_CompanyID_Company_ID] FOREIGN KEY ([CompanyID]) REFERENCES [Companies] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Employee_CompanyID_Company_ID' CREATE INDEX [IX_FK_Employee_CompanyID_Company_ID] ON [Employees] ([CompanyID]); GO -- Creating foreign key on [BossEmployeeID] in table 'Employees' ALTER TABLE [Employees] ADD CONSTRAINT [FK_Employee_BossEmployeeID_Employee_ID] FOREIGN KEY ([BossEmployeeID]) REFERENCES [Employees] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Employee_BossEmployeeID_Employee_ID' CREATE INDEX [IX_FK_Employee_BossEmployeeID_Employee_ID] ON [Employees] ([BossEmployeeID]); GO -- Creating foreign key on [PersonID] in table 'Employees' ALTER TABLE [Employees] ADD CONSTRAINT [FK_Employee_PersonID_Person_ID] FOREIGN KEY ([PersonID]) REFERENCES [People] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Employee_PersonID_Person_ID' CREATE INDEX [IX_FK_Employee_PersonID_Person_ID] ON [Employees] ([PersonID]); GO -- -------------------------------------------------- -- Script has ended -- --------------------------------------------------

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  • What is the proper way to create a recursive entity in the Entity Framework?

    - by Orion Adrian
    I'm currently using VS 2010 RC, and I'm trying to create a model that contains a recursive self-referencing entity. Currently when I import the entity from the model I get an error indicating that the parent property cannot be part of the association because it's set to 'Computed' or 'Identity', though I'm not sure why it does it that way. I've been hand-editing the file to get around that error, but then the model simply doesn't work. What is the proper way to get recursive entities to work in the Entity Framework. CREATE TABLE [dbo].[Appointments]( [AppointmentId] [int] IDENTITY(1,1) NOT NULL, [Description] [nvarchar](1024) NULL, [Start] [datetime] NOT NULL, [End] [datetime] NOT NULL, [Username] [varchar](50) NOT NULL, [RecurrenceRule] [nvarchar](1024) NULL, [RecurrenceState] [varchar](20) NULL, [RecurrenceParentId] [int] NULL, [Annotations] [nvarchar](50) NULL, [Application] [nvarchar](100) NOT NULL, CONSTRAINT [PK_Appointments] PRIMARY KEY CLUSTERED ( [AppointmentId] ASC ) ) GO ALTER TABLE [dbo].[Appointments] WITH CHECK ADD CONSTRAINT [FK_Appointments_ParentAppointments] FOREIGN KEY([RecurrenceParentId]) REFERENCES [dbo].[Appointments] ([AppointmentId]) GO ALTER TABLE [dbo].[Appointments] CHECK CONSTRAINT [FK_Appointments_ParentAppointments] GO

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  • I am not able to create foreign key in mysql Error 150. Please help

    - by Shantanu Gupta
    i am trying to create a foreign key in my table. But when i executes my query it shows me error 150 Error Code : 1005 Can't create table '.\vts#sql-6ec_1.frm' (errno: 150) (0 ms taken) My Queries are Query to create a foreign Key alter table `vts`.`tblguardian` add constraint `FK_tblguardian` FOREIGN KEY (`GuardianPickPointId`) REFERENCES `tblpickpoint` (`PickPointId`) Primary Key table CREATE TABLE `tblpickpoint` ( `PickPointId` int(4) NOT NULL auto_increment, `PickPointName` varchar(500) default NULL, `PickPointLabel` varchar(500) default NULL, `PickPointLatLong` varchar(100) NOT NULL, PRIMARY KEY (`PickPointId`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 CHECKSUM=1 DELAY_KEY_WRITE=1 ROW_FORMAT=DYNAMIC Foreign Key Table CREATE TABLE `tblguardian` ( `GuardianId` int(4) NOT NULL auto_increment, `GuardianName` varchar(500) default NULL, `GuardianAddress` varchar(500) default NULL, `GuardianMobilePrimary` varchar(15) NOT NULL, `GuardianMobileSecondary` varchar(15) default NULL, `GuardianPickPointId` varchar(100) default NULL, PRIMARY KEY (`GuardianId`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1

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  • How can I do a right outer join where both tables have a where clause?

    - by cdeszaq
    Here's the scenario: I have 2 tables: CREATE TABLE dbo.API_User ( id int NOT NULL, name nvarchar(255) NOT NULL, authorization_key varchar(255) NOT NULL, is_active bit NOT NULL ) ON [PRIMARY] CREATE TABLE dbo.Single_Sign_On_User ( id int NOT NULL IDENTITY (1, 1), API_User_id int NOT NULL, external_id varchar(255) NOT NULL, user_id int NULL ) ON [PRIMARY] What I am trying to return is the following: is_active for a given authorization_key The Single_Sign_On_User.id that matches the external_id/API_User_id pair if it exists or NULL if there is no such pair When I try this query: SELECT Single_Sign_On_User.id, API_User.is_active FROM API_User LEFT OUTER JOIN Single_Sign_On_User ON Single_Sign_On_User.API_User_id = API_User.id WHERE Single_Sign_On_User.external_id = 'test_ext_id' AND API_User.authorization_key = 'test' where the "test" API_User record exists but the "test_ext_id" record does not, and with no other values in either table, I get no records returned. When I use: SELECT Single_Sign_On_User.id, API_User.is_active FROM API_User LEFT OUTER JOIN Single_Sign_On_User ON Single_Sign_On_User.API_User_id = API_User.id WHERE API_User.authorization_key = 'test' I get the results I expect (NULL, 1), but that query doesn't allow me to find the "test_ext_id" record if it exists but would give me all records associated with the "test" API_User record. How can I get the results I am after?

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  • Execution Plan Optimization when where clause is removed then added back

    - by nmushov
    I have a stored procedure that uses a table valued function which executes in 9 seconds. If I alter the table valued function and remove the where clause, the stored procedure executes in 3 seconds. If I add the where clause back, the query still executes in 3 seconds. I took a look at the execution plans and it appears that after I remove the where clause, the execution plan includes parallelism and the scan count for 2 of my tables drops for 50000 and 65000 down to 5 and 3. After I add the where clause back, the optimized execution plan still runs unless I run DBCC FREEPROCCACHE. Questions 1. Why would SQL Server start using the optimized execution plan for both queries only when I first remove the where clause? Is there a way to force SQL Server to use this execution plan? Also, this is a paramaterized all-in-one query that uses the (Parameter is null or Parameter) in the where clause, which I believe is bad for performance. RETURNS TABLE AS RETURN ( SELECT TOP (@PageNumber * @PageSize) CASE WHEN @SortOrder = 'Expensive' THEN ROW_NUMBER() OVER (ORDER BY SellingPrice DESC) WHEN @SortOrder = 'Inexpensive' THEN ROW_NUMBER() OVER (ORDER BY SellingPrice ASC) WHEN @SortOrder = 'LowMiles' THEN ROW_NUMBER() OVER (ORDER BY Mileage ASC) WHEN @SortOrder = 'HighMiles' THEN ROW_NUMBER() OVER (ORDER BY Mileage DESC) WHEN @SortOrder = 'Closest' THEN ROW_NUMBER() OVER (ORDER BY P1.Distance ASC) WHEN @SortOrder = 'Newest' THEN ROW_NUMBER() OVER (ORDER BY [Year] DESC) WHEN @SortOrder = 'Oldest' THEN ROW_NUMBER() OVER (ORDER BY [Year] ASC) ELSE ROW_NUMBER() OVER (ORDER BY InventoryID ASC) END as rn, P1.InventoryID, P1.SellingPrice, P1.Distance, P1.Mileage, Count(*) OVER () RESULT_COUNT, dimCarStatus.[year] FROM (SELECT InventoryID, SellingPrice, Zip.Distance, Mileage, ColorKey, CarStatusKey, CarKey FROM facInventory JOIN @ZipCodes Zip ON Zip.DealerKey = facInventory.DealerKey) as P1 JOIN dimColor ON dimColor.ColorKey = P1.ColorKey JOIN dimCarStatus ON dimCarStatus.CarStatusKey = P1.CarStatusKey JOIN dimCar ON dimCar.CarKey = P1.CarKey WHERE (@ExteriorColor is NULL OR dimColor.ExteriorColor like @ExteriorColor) AND (@InteriorColor is NULL OR dimColor.InteriorColor like @InteriorColor) AND (@Condition is NULL OR dimCarStatus.Condition like @Condition) AND (@Year is NULL OR dimCarStatus.[Year] like @Year) AND (@Certified is NULL OR dimCarStatus.Certified like @Certified) AND (@Make is NULL OR dimCar.Make like @Make) AND (@ModelCategory is NULL OR dimCar.ModelCategory like @ModelCategory) AND (@Model is NULL OR dimCar.Model like @Model) AND (@Trim is NULL OR dimCar.Trim like @Trim) AND (@BodyType is NULL OR dimCar.BodyType like @BodyType) AND (@VehicleTypeCode is NULL OR dimCar.VehicleTypeCode like @VehicleTypeCode) AND (@MinPrice is NULL OR P1.SellingPrice >= @MinPrice) AND (@MaxPrice is NULL OR P1.SellingPrice < @MaxPrice) AND (@Mileage is NULL OR P1.Mileage < @Mileage) ORDER BY CASE WHEN @SortOrder = 'Expensive' THEN -SellingPrice WHEN @SortOrder = 'Inexpensive' THEN SellingPrice WHEN @SortOrder = 'LowMiles' THEN Mileage WHEN @SortOrder = 'HighMiles' THEN -Mileage WHEN @SortOrder = 'Closest' THEN P1.Distance WHEN @SortOrder = 'Newest' THEN -[YEAR] WHEN @SortOrder = 'Oldest' THEN [YEAR] ELSE InventoryID END )

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  • I am not able to drop foreign key in mysql Error 150. Please help

    - by Shantanu Gupta
    i am trying to create a foreign key in my table. But when i executes my query it shows me error 150 Error Code : 1005 Can't create table '.\vts#sql-6ec_1.frm' (errno: 150) (0 ms taken) My Queries are Query to create a foreign Key alter table `vts`.`tblguardian` add constraint `FK_tblguardian` FOREIGN KEY (`GuardianPickPointId`) REFERENCES `tblpickpoint` (`PickPointId`) EDIT: Now I am trying to drop this constraint But it fails again and shows me same error as it was giving when i was trying to create foreign key. alter table `vts`.`tblguardian` drop index `FK_tblguardian` Primary Key table CREATE TABLE `tblpickpoint` ( `PickPointId` int(4) NOT NULL auto_increment, `PickPointName` varchar(500) default NULL, `PickPointLabel` varchar(500) default NULL, `PickPointLatLong` varchar(100) NOT NULL, PRIMARY KEY (`PickPointId`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 CHECKSUM=1 DELAY_KEY_WRITE=1 ROW_FORMAT=DYNAMIC Foreign Key Table CREATE TABLE `tblguardian` ( `GuardianId` int(4) NOT NULL auto_increment, `GuardianName` varchar(500) default NULL, `GuardianAddress` varchar(500) default NULL, `GuardianMobilePrimary` varchar(15) NOT NULL, `GuardianMobileSecondary` varchar(15) default NULL, `GuardianPickPointId` int(4) default NULL, PRIMARY KEY (`GuardianId`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1

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  • Database for survey

    - by zfm
    One of my job now is to design a database for a survey. Let's say we have a series of questions (web-based), in which one page contains one question. Not every person will be given the same questions, those are based on their previous answers and also randomness. I would like to know whether it is better to have database like this user question answer userX question1 answer1A userX question2 answer2C userX question5 answer5F userY question1 answer1B userY question3 answer3B userY question6 answer6D ... or user q1 q2 q3 q4 q5 q6 userX 1A 2C null null 5F null userY 1B null 3B null null 6D ... My idea here is, using the second approach seems better, however I would like to know whether updating the table is (much) slower than inserting a new row? Also with the first approach, I can omit having some null answers. The total questions given are fix, the client wont add any more question later on. So my question is, what will you do if you were me?

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  • PHP Moving mySQL Tree Node

    - by TK
    I am having trouble trying to move sub nodes or parent nodes up or down... not that good at math. CREATE TABLE IF NOT EXISTS `pages` ( page-id mediumint(8) unsigned NOT NULL AUTO_INCREMENT, page-left mediumint(8) unsigned NOT NULL, page-right smallint(8) unsigned NOT NULL, page-title text NOT NULL, page-content text NOT NULL, page-time int(11) unsigned NOT NULL, page-slug text NOT NULL, page-template text NOT NULL, page-parent mediumint(8) unsigned NOT NULL, page-type text NOT NULL, PRIMARY KEY (page-id) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 ; INSERT INTO pages (page-id, page-left, page-right, page-title, page-content, page-time, page-slug, page-template, page-parent, page-type) VALUES (17, 1, 6, '1', '', 0, 'PARENT', '', 0, ''), (18, 2, 5, '2', '', 0, 'SUB', '', 17, ''), (19, 3, 4, '3', '', 0, 'SUB-SUB', '', 18, ''), (20, 7, 8, '5', '', 0, 'TEST', '', 0, ''); As example how would I move TEST up above PARENT and say move SUB down below SUB-SUB by playing with the page-left/page-right IDs? Code is not required just help with the SQL concept or math for it, would help me understand how to move it better...

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  • Data Access from single table in sql server 2005 is too slow

    - by Muhammad Kashif Nadeem
    Following is the script of table. Accessing data from this table is too slow. SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[Emails]( [id] [int] IDENTITY(1,1) NOT NULL, [datecreated] [datetime] NULL CONSTRAINT [DF_Emails_datecreated] DEFAULT (getdate()), [UID] [nvarchar](250) COLLATE Latin1_General_CI_AS NULL, [From] [nvarchar](100) COLLATE Latin1_General_CI_AS NULL, [To] [nvarchar](100) COLLATE Latin1_General_CI_AS NULL, [Subject] [nvarchar](max) COLLATE Latin1_General_CI_AS NULL, [Body] [nvarchar](max) COLLATE Latin1_General_CI_AS NULL, [HTML] [nvarchar](max) COLLATE Latin1_General_CI_AS NULL, [AttachmentCount] [int] NULL, [Dated] [datetime] NULL ) ON [PRIMARY] Following query takes 50 seconds to fetch data. select id, datecreated, UID, [From], [To], Subject, AttachmentCount, Dated from emails If I include Body and Html in select then time is event worse. indexes are on: id unique clustered From Non unique non clustered To Non unique non clustered Tabls has currently 180000+ records. There might be 100,000 records each month so this will become more slow as time will pass. Does splitting data into two table will solve the problem? What other indexes should be there?

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  • how to design this relation in a DB schema

    - by raticulin
    I have a table Car in my db, one of the columns is purchaseDate. I want to be able to tag every car with a number of Policies (limited to 10 policies). Each policy has a time to life (ttl, a duration of time, like '5 years', '10 months' etc), that is, for how long since the car's purchaseDate the policy can be applied. I need to perform the following actions: when inserting a Car, it will be set with a number of Policies (at least one is set) sometimes a Car will be updated to add/remove a Policy searches must be done taking into account date/policies, for example: 'select all cars that are not covered by any policy as of today' My current design is (pol0..pol9 are the policies): CREATE TABLE Car ( id int NOT NULL IDENTITY(1,1), purchaseDate datetime NOT NULL, //more stuff... pol0 smallint default NULL, pol1 smallint default NULL, pol2 smallint default NULL, pol3 smallint default NULL, pol4 smallint default NULL, pol5 smallint default NULL, pol6 smallint default NULL, pol7 smallint default NULL, pol8 smallint default NULL, pol9 smallint default NULL, PRIMARY KEY (id) ) CREATE TABLE Policy ( id smallint NOT NULL, name varchar(50) collate Latin1_General_BIN NOT NULL, ttl varchar(100) collate Latin1_General_BIN NOT NULL, PRIMARY KEY (id) ) The problem I am facing is that the sql to perform the query above is a nightmare to write. As I don't know in which column each policy can be, so I have to check all columns for every policy etc etc. So I am wondering wether it is worth changing this. My questions are: The smallint as Policy id was chosen instead of an 'int IDENTITY' in order to save some space as there are going to be millions of Car records. It just adds complexity when creating a Policy as we must handle the id etc. Was it worth doing this? I am thinking that maybe there is a much better design? Obviously we could move the policy/car relation to its own table CarPolicy, benefits would be: no limit on 10 policies per car adding/removing etc much easier when only the default policy is applied (when no others are applied one called Default policy is applied), we could signal that by not having any entry in CarPolicy, now this is just done inserting the Default policy id in one of the columns. The cons are that we would need to change the DB, ORM classes etc. What would you recommend? Maybe there is another smart way to implement this that we are not aware without using the CarPolicy table?

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  • insert into several inheritance tables with OUTPUT - sql servr 2005

    - by csetzkorn
    Hi, I have a bunch of items – for simplicity reasons – a flat table with unique names seeded via bulk insert: create table #items ( ItemName NVARCHAR(255) ) The database has this structure: create table Statements ( Id INT IDENTITY NOT NULL, Version INT not null, FurtherDetails varchar(max) null, ProposalDateTime DATETIME null, UpdateDateTime DATETIME null, ProposerFk INT null, UpdaterFk INT null, primary key (Id) ) create table Item ( StatementFk INT not null, ItemName NVARCHAR(255) null, primary key (StatementFk) ) Here Item is a child of Statement (inheritance). I would like to insert items in #items using a set based approach (avoiding triggers and loops). Can this be achieved with OUTPUT in my scenario. A ‘loop based’ approach is just too slow where I use something like this: insert into Statements (Version, FurtherDetails, ProposalDateTime, UpdateDateTime, ProposerFk, UpdaterFk) VALUES (1, null, getdate(), getdate(), @user_id, @user_id) etc. This is a start for the OUTPUT based approach – but I am not sure whether this would work in my case as ItemName is only inserted into Item: insert into Statements ( Version, FurtherDetails, ProposalDateTime, UpdateDateTime, ProposerFk, UpdaterFk ) output inserted.Id ... ??? Thanks. Best wishes, Christian

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  • Values of generated column not appearing in table

    - by msh210
    I'm using mysql version 5.1.41-3ubuntu12.10 (Ubuntu). mysql> show create table tt\G *************************** 1. row *************************** Table: tt Create Table: CREATE TABLE `tt` ( `pz` int(8) DEFAULT NULL, `os` varchar(8) DEFAULT NULL, `uz` int(11) NOT NULL, `p` bigint(21) NOT NULL DEFAULT '0', `c` decimal(23,0) DEFAULT NULL, KEY `pz` (`pz`), KEY `uz` (`uz`), KEY `os` (`os`), KEY `pz_2` (`pz`,`uz`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 1 row in set (0.00 sec) mysql> select pz,uz,pz*uz, -> if(pz*uz,1,.5), -> left(pz,2) pl,left(lpad(uz,5,0),2) ul, -> p from tt limit 10; +-------+----+-------+----------------+--------+----+--------+ | pz | uz | pz*uz | if(pz*uz,1,.5) | pl | ul | p | +-------+----+-------+----------------+--------+----+--------+ | NULL | 0 | NULL | 0.5 | NULL | 00 | 4080 | | NULL | 0 | NULL | 0.5 | NULL | 00 | 323754 | | 89101 | 0 | 0 | 0.5 | 89 | 00 | 6880 | | 0 | 0 | 0 | 0.5 | 0 | 00 | 11591 | | 89110 | 0 | 0 | 0.5 | 89 | 00 | 72 | | 78247 | 0 | 0 | 0.5 | 78 | 00 | 27 | | 90062 | 0 | 0 | 0.5 | 90 | 00 | 5 | | 63107 | 0 | 0 | 0.5 | 63 | 00 | 4 | | NULL | 0 | NULL | 0.5 | NULL | 00 | 54561 | | 94102 | 0 | 0 | 0.5 | 94 | 00 | 12499 | +-------+----+-------+----------------+--------+----+--------+ So far so good. As you see, 0.5 appears as a value of if(pz*uz,1,.5). The problem is: mysql> select os, -> if(pz*uz,left(pz,2)<=>left(lpad(uz,5,0),2),.5) uptwo, -> if(pz*uz,left(pz,3)<=>left(lpad(uz,5,0),3),.5) upthree, -> sum(p) p,sum(c) c -> from tt t -> group by os,uptwo,upthree order by null; +----+-------+---------+---------+-------+ | os | uptwo | upthree | p | c | +----+-------+---------+---------+-------+ | u | 1 | 1 | 52852 | 318 | | i | 1 | 1 | 7046563 | 21716 | | m | 1 | 1 | 1252166 | 7337 | | i | 0 | 0 | 1830284 | 4033 | | m | 0 | 0 | 294612 | 1714 | | i | 1 | 0 | 911486 | 3560 | | m | 1 | 0 | 145182 | 1136 | | u | 0 | 0 | 12144 | 23 | | u | 1 | 0 | 1571 | 8 | +----+-------+---------+---------+-------+ Although I group by uptwo, 0.5 doesn't appear in that column. What happened to the 0.5 values? Edit: As noted in the comments to Todd Gibson's answer, I also tried it with if(pz*uz,cast(left(pz,2)<=>left(lpad(uz,5,0),2) as decimal),.5) instead of if(pz*uz,left(pz,2)<=>left(lpad(uz,5,0),2),.5), but it, too, didn't work.

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  • Can an asynchronously fired event run synchronously on a form?

    - by cyclotis04
    [VS 2010 Beta with .Net Framework 3.5] I've written a C# component to asynchronously monitor a socket and raise events when data is received. I set the VB form to show message boxes when the event is raised. What I've noticed is that when the component raises the event synchronously, the message box blocks the component code and locks the form until the user closes the message. When it's raised asynchronously, it neither blocks the code, nor locks the form. What I want is a way to raise an event in such a way that it does not block the code, but is called on the same thread as the form (so that it locks the form until the user selects an option.) Can you help me out? Thanks. [Component] using System; using System.Threading; using System.ComponentModel; namespace mySpace { public delegate void SyncEventHandler(object sender, SyncEventArgs e); public delegate void AsyncEventHandler(object sender, AsyncEventArgs e); public class myClass { readonly object syncEventLock = new object(); readonly object asyncEventLock = new object(); SyncEventHandler syncEvent; AsyncEventHandler asyncEvent; private delegate void WorkerDelegate(string strParam, int intParam); public void DoWork(string strParam, int intParam) { OnSyncEvent(new SyncEventArgs()); AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(null); WorkerDelegate delWorker = new WorkerDelegate(ClientWorker); IAsyncResult result = delWorker.BeginInvoke(strParam, intParam, null, null); } private void ClientWorker(string strParam, int intParam) { Thread.Sleep(2000); OnAsyncEvent(new AsyncEventArgs()); OnAsyncEvent(new AsyncEventArgs()); } public event SyncEventHandler SyncEvent { add { lock (syncEventLock) syncEvent += value; } remove { lock (syncEventLock) syncEvent -= value; } } public event AsyncEventHandler AsyncEvent { add { lock (asyncEventLock) asyncEvent += value; } remove { lock (asyncEventLock) asyncEvent -= value; } } protected void OnSyncEvent(SyncEventArgs e) { SyncEventHandler handler; lock (syncEventLock) handler = syncEvent; if (handler != null) handler(this, e, null, null); // Blocks and locks //if (handler != null) handler.BeginInvoke(this, e, null, null); // Neither blocks nor locks } protected void OnAsyncEvent(AsyncEventArgs e) { AsyncEventHandler handler; lock (asyncEventLock) handler = asyncEvent; //if (handler != null) handler(this, e, null, null); // Blocks and locks if (handler != null) handler.BeginInvoke(this, e, null, null); // Neither blocks nor locks } } } [Form] Imports mySpace Public Class Form1 Public WithEvents component As New mySpace.myClass() Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click component.DoWork("String", 1) End Sub Private Sub component_SyncEvent(ByVal sender As Object, ByVal e As pbxapi.SyncEventArgs) Handles component.SyncEvent MessageBox.Show("Synchronous event", "Raised:", MessageBoxButtons.OK) End Sub Private Sub component_AsyncEvent(ByVal sender As Object, ByVal e As pbxapi.AsyncEventArgs) Handles component.AsyncEvent MessageBox.Show("Asynchronous event", "Raised:", MessageBoxButtons.OK) End Sub End Class

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  • Error on SQL insert statement

    - by Ashley Stewart
    I exported a recordset from one database into a csv file, and when I try to import it into another using mysql workbench I keep this this error message: Executing SQL script in server ERROR: Error 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' 'Lord it Over', 'Ben', '1993-03-01', 'TRC', NULL, 1983, '1999-09-01', 'NULL', '' at line 1 INSERT INTO `TRC`.`horse` (`horse_id`, `registered_name`, `stable_name`, `arrival_date`, `last_known_location`, `is_ex_racer`, `birth_year`, `death_date`, `horse_comments`, `sex`, `referral_date`, `horse_height`, `arrival_weight`, `passport_no`, `microchip_no`, `is_on_waiting_list`) VALUES (, 'Lord it Over', 'Ben', '1993-03-01', 'TRC', NULL, 1983, '1999-09-01', 'NULL', 'NULL', 'NULL', NULL, NULL, 'NULL', 'NULL', 0) SQL script execution finished: statements: 29 succeeded, 1 failed Fetching back view definitions in final form. Nothing to fetch Any help would be appreciated as their appears to be no errors as far as I can see.

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  • MySQL multiple dependent subqueries, painfully slow

    - by matt80
    I have a working query that retrieves the data that I need, but unfortunately it is painfully slow (runs over 3 minutes). I have indexes in place, but I think the problem is the multiple dependent subqueries. I've been trying to rewrite the query using joins but I can't seem to get it to work. Any help would be greatly appreciated. The tables: Basically, I have 2 tables. The first (prices) holds the prices of items in a store. Each row is the price of an item that day, and new rows are added every day with an updated price. The second table (watches_US) holds the item information (name, description, etc). CREATE TABLE `prices` ( `prices_id` int(11) NOT NULL auto_increment, `prices_locale` enum('CA','DE','FR','JP','UK','US') NOT NULL default 'US', `prices_watches_ID` char(10) NOT NULL, `prices_date` datetime NOT NULL, `prices_am` varchar(10) default NULL, `prices_new` varchar(10) default NULL, `prices_used` varchar(10) default NULL, PRIMARY KEY (`prices_id`), KEY `prices_am` (`prices_am`), KEY `prices_locale` (`prices_locale`), KEY `prices_watches_ID` (`prices_watches_ID`), KEY `prices_date` (`prices_date`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=61764 ; CREATE TABLE `watches_US` ( `watches_ID` char(10) NOT NULL, `watches_date_added` datetime NOT NULL, `watches_last_update` datetime default NULL, `watches_title` varchar(255) default NULL, `watches_small_image_height` int(11) default NULL, `watches_small_image_width` int(11) default NULL, `watches_description` text, PRIMARY KEY (`watches_ID`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; The query retrieves the last 10 prices changes over a period of 30 hours, ordered by the size of the price change. So I have subqueries to get the newest price, the oldest price within 30 hours, and then to calculate the price change. Here's the query: SELECT watches_US.*, prices.*, watches_US.watches_ID as current_ID, ( SELECT prices_am FROM prices WHERE prices_watches_ID = current_ID AND prices_locale = 'US' ORDER BY prices_date DESC LIMIT 1 ) as new_price, ( SELECT prices_date FROM prices WHERE prices_watches_ID = current_ID AND prices_locale = 'US' ORDER BY prices_date DESC LIMIT 1 ) as new_price_date, ( SELECT prices_am FROM prices WHERE ( prices_watches_ID = current_ID AND prices_locale = 'US') AND ( prices_date >= DATE_SUB(new_price_date,INTERVAL 30 HOUR) ) ORDER BY prices_date ASC LIMIT 1 ) as old_price, ( SELECT ROUND(((new_price - old_price)/old_price)*100,2) ) as percent_change, ( SELECT (new_price - old_price) ) as absolute_change FROM watches_US LEFT OUTER JOIN prices ON prices.prices_watches_ID = watches_US.watches_ID WHERE ( prices_locale = 'US' ) AND ( prices_am IS NOT NULL ) AND ( prices_am != '' ) HAVING ( old_price IS NOT NULL ) AND ( old_price != 0 ) AND ( old_price != '' ) AND ( absolute_change < 0 ) AND ( prices.prices_date = new_price_date ) ORDER BY absolute_change ASC LIMIT 10 How would I rewrite this to use joins instead, or otherwise optimize this so it doesn't take over 3 minutes to get a result? Any help would be greatly appreciated! Thank you kindly.

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  • Linq: comparison with nonexisting value should not cause the exception, but it does

    - by Seacat
    Hello, Given I don't know if the parameter will be null or not and I want to use it in the following way: if Param != null then compare with its id if Param == null then compare with null. Something like that: var c = from cat in context.Categories where ParamCat != null && cat.ParentId == ParamCat.Id || ParamCat == null && cat.ParentId == null select c; If ParamCat is null as soon as I try to get something from c (for example c.Count()) it throws the exception. Usually when we use some kind of condition it stop comparison as soon as condition fail especially if we use AND. For example this code will not cause any exception: if (ParamCat != null && cat.ParentId == RaramCat.Id) { } If so, why the linq code above throw exception? (Null reference) Thanks

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  • How can I make my generic comparer (IComparer) handle nulls? [closed]

    - by Nick G
    Hi, I'm trying to write a generic object comparer for sorting, but I have noticed it does not handle the instance where one of the values it's comparing is null. When an object is null, I want it to treat it the same as the empty string. I've tried setting the null values to String.Empty but then I get an error of "Object must be of type String" when calling CompareTo() on it. public int Compare(T x, T y) { PropertyInfo propertyInfo = typeof(T).GetProperty(sortExpression); IComparable obj1 = (IComparable)propertyInfo.GetValue(x, null); IComparable obj2 = (IComparable)propertyInfo.GetValue(y, null); if (obj1 == null) obj1 = String.Empty; // This doesn't work! if (obj2 == null) obj2 = String.Empty; // This doesn't work! if (SortDirection == SortDirection.Ascending) return obj1.CompareTo(obj2); else return obj2.CompareTo(obj1); } I'm pretty stuck with this now! Any help would be appreciated.

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  • How can I do a left outer join where both tables have a where clause?

    - by cdeszaq
    Here's the scenario: I have 2 tables: CREATE TABLE dbo.API_User ( id int NOT NULL, name nvarchar(255) NOT NULL, authorization_key varchar(255) NOT NULL, is_active bit NOT NULL ) ON [PRIMARY] CREATE TABLE dbo.Single_Sign_On_User ( id int NOT NULL IDENTITY (1, 1), API_User_id int NOT NULL, external_id varchar(255) NOT NULL, user_id int NULL ) ON [PRIMARY] What I am trying to return is the following: is_active for a given authorization_key The Single_Sign_On_User.id that matches the external_id/API_User_id pair if it exists or NULL if there is no such pair When I try this query: SELECT Single_Sign_On_User.id, API_User.is_active FROM API_User LEFT OUTER JOIN Single_Sign_On_User ON Single_Sign_On_User.API_User_id = API_User.id WHERE Single_Sign_On_User.external_id = 'test_ext_id' AND API_User.authorization_key = 'test' where the "test" API_User record exists but the "test_ext_id" record does not, and with no other values in either table, I get no records returned. When I use: SELECT Single_Sign_On_User.id, API_User.is_active FROM API_User LEFT OUTER JOIN Single_Sign_On_User ON Single_Sign_On_User.API_User_id = API_User.id WHERE API_User.authorization_key = 'test' I get the results I expect (NULL, 1), but that query doesn't allow me to find the "test_ext_id" record if it exists but would give me all records associated with the "test" API_User record. How can I get the results I am after?

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  • how to set the tab order for the UI controls in win 32?

    - by Rakesh
    hello all I have a small dialog which I created dynamically, which has a textbox and a button..if the user presses the TAB key it has to switch between the two control(textbox and button)...I tried using SetwindowPos...but it doesnt seem to solve my problem...please give me a solution for this..in the below code..I also tried to include the mainwindow in the taborder..still it doesnt work //dialog creation HWND dialogHandle = CreateWindowEx(0,WC_DIALOG,L"Security Alert",WS_OVERLAPPEDWINDOW|WS_VISIBLE,600,300,280,160,NULL,NULL,NULL,NULL); //create textboxcontrol within the dialog HWND textBoxHandle = CreateWindowEx(WS_EX_CLIENTEDGE,L"EDIT",L"",WS_CHILD|WS_VISIBLE |ES_PASSWORD | WS_TABSTOP,123,48,110,25,dialogHandle,(HMENU)IDD_TEXTBOX,NULL,NULL); //create button HWND buttonHandle = CreateWindowEx(NULL,L"Button",L"OK",WS_CHILD|WS_VISIBLE| WS_TABSTOP,151,85,85,25,dialogHandle,(HMENU)ID_PASSWORD_OK,NULL,NULL); //setwindowpos SetWindowPos(NULL,textBoxHandle,0,0,0,0,SWP_NOMOVE|SWP_NOSIZE); SetWindowPos(textBoxHandle,buttonHandle,0,0,0,0,SWP_NOMOVE|SWP_NOSIZE);

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  • A ToDynamic() Extension Method For Fluent Reflection

    - by Dixin
    Recently I needed to demonstrate some code with reflection, but I felt it inconvenient and tedious. To simplify the reflection coding, I created a ToDynamic() extension method. The source code can be downloaded from here. Problem One example for complex reflection is in LINQ to SQL. The DataContext class has a property Privider, and this Provider has an Execute() method, which executes the query expression and returns the result. Assume this Execute() needs to be invoked to query SQL Server database, then the following code will be expected: using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // Executes the query. Here reflection is required, // because Provider, Execute(), and ReturnValue are not public members. IEnumerable<Product> results = database.Provider.Execute(query.Expression).ReturnValue; // Processes the results. foreach (Product product in results) { Console.WriteLine("{0}, {1}", product.ProductID, product.ProductName); } } Of course, this code cannot compile. And, no one wants to write code like this. Again, this is just an example of complex reflection. using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // database.Provider PropertyInfo providerProperty = database.GetType().GetProperty( "Provider", BindingFlags.NonPublic | BindingFlags.GetProperty | BindingFlags.Instance); object provider = providerProperty.GetValue(database, null); // database.Provider.Execute(query.Expression) // Here GetMethod() cannot be directly used, // because Execute() is a explicitly implemented interface method. Assembly assembly = Assembly.Load("System.Data.Linq"); Type providerType = assembly.GetTypes().SingleOrDefault( type => type.FullName == "System.Data.Linq.Provider.IProvider"); InterfaceMapping mapping = provider.GetType().GetInterfaceMap(providerType); MethodInfo executeMethod = mapping.InterfaceMethods.Single(method => method.Name == "Execute"); IExecuteResult executeResult = executeMethod.Invoke(provider, new object[] { query.Expression }) as IExecuteResult; // database.Provider.Execute(query.Expression).ReturnValue IEnumerable<Product> results = executeResult.ReturnValue as IEnumerable<Product>; // Processes the results. foreach (Product product in results) { Console.WriteLine("{0}, {1}", product.ProductID, product.ProductName); } } This may be not straight forward enough. So here a solution will implement fluent reflection with a ToDynamic() extension method: IEnumerable<Product> results = database.ToDynamic() // Starts fluent reflection. .Provider.Execute(query.Expression).ReturnValue; C# 4.0 dynamic In this kind of scenarios, it is easy to have dynamic in mind, which enables developer to write whatever code after a dot: using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // database.Provider dynamic dynamicDatabase = database; dynamic results = dynamicDatabase.Provider.Execute(query).ReturnValue; } This throws a RuntimeBinderException at runtime: 'System.Data.Linq.DataContext.Provider' is inaccessible due to its protection level. Here dynamic is able find the specified member. So the next thing is just writing some custom code to access the found member. .NET 4.0 DynamicObject, and DynamicWrapper<T> Where to put the custom code for dynamic? The answer is DynamicObject’s derived class. I first heard of DynamicObject from Anders Hejlsberg's video in PDC2008. It is very powerful, providing useful virtual methods to be overridden, like: TryGetMember() TrySetMember() TryInvokeMember() etc.  (In 2008 they are called GetMember, SetMember, etc., with different signature.) For example, if dynamicDatabase is a DynamicObject, then the following code: dynamicDatabase.Provider will invoke dynamicDatabase.TryGetMember() to do the actual work, where custom code can be put into. Now create a type to inherit DynamicObject: public class DynamicWrapper<T> : DynamicObject { private readonly bool _isValueType; private readonly Type _type; private T _value; // Not readonly, for value type scenarios. public DynamicWrapper(ref T value) // Uses ref in case of value type. { if (value == null) { throw new ArgumentNullException("value"); } this._value = value; this._type = value.GetType(); this._isValueType = this._type.IsValueType; } public override bool TryGetMember(GetMemberBinder binder, out object result) { // Searches in current type's public and non-public properties. PropertyInfo property = this._type.GetTypeProperty(binder.Name); if (property != null) { result = property.GetValue(this._value, null).ToDynamic(); return true; } // Searches in explicitly implemented properties for interface. MethodInfo method = this._type.GetInterfaceMethod(string.Concat("get_", binder.Name), null); if (method != null) { result = method.Invoke(this._value, null).ToDynamic(); return true; } // Searches in current type's public and non-public fields. FieldInfo field = this._type.GetTypeField(binder.Name); if (field != null) { result = field.GetValue(this._value).ToDynamic(); return true; } // Searches in base type's public and non-public properties. property = this._type.GetBaseProperty(binder.Name); if (property != null) { result = property.GetValue(this._value, null).ToDynamic(); return true; } // Searches in base type's public and non-public fields. field = this._type.GetBaseField(binder.Name); if (field != null) { result = field.GetValue(this._value).ToDynamic(); return true; } // The specified member is not found. result = null; return false; } // Other overridden methods are not listed. } In the above code, GetTypeProperty(), GetInterfaceMethod(), GetTypeField(), GetBaseProperty(), and GetBaseField() are extension methods for Type class. For example: internal static class TypeExtensions { internal static FieldInfo GetBaseField(this Type type, string name) { Type @base = type.BaseType; if (@base == null) { return null; } return @base.GetTypeField(name) ?? @base.GetBaseField(name); } internal static PropertyInfo GetBaseProperty(this Type type, string name) { Type @base = type.BaseType; if (@base == null) { return null; } return @base.GetTypeProperty(name) ?? @base.GetBaseProperty(name); } internal static MethodInfo GetInterfaceMethod(this Type type, string name, params object[] args) { return type.GetInterfaces().Select(type.GetInterfaceMap).SelectMany(mapping => mapping.TargetMethods) .FirstOrDefault( method => method.Name.Split('.').Last().Equals(name, StringComparison.Ordinal) && method.GetParameters().Count() == args.Length && method.GetParameters().Select( (parameter, index) => parameter.ParameterType.IsAssignableFrom(args[index].GetType())).Aggregate( true, (a, b) => a && b)); } internal static FieldInfo GetTypeField(this Type type, string name) { return type.GetFields( BindingFlags.GetField | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic).FirstOrDefault( field => field.Name.Equals(name, StringComparison.Ordinal)); } internal static PropertyInfo GetTypeProperty(this Type type, string name) { return type.GetProperties( BindingFlags.GetProperty | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic).FirstOrDefault( property => property.Name.Equals(name, StringComparison.Ordinal)); } // Other extension methods are not listed. } So now, when invoked, TryGetMember() searches the specified member and invoke it. The code can be written like this: dynamic dynamicDatabase = new DynamicWrapper<NorthwindDataContext>(ref database); dynamic dynamicReturnValue = dynamicDatabase.Provider.Execute(query.Expression).ReturnValue; This greatly simplified reflection. ToDynamic() and fluent reflection To make it even more straight forward, A ToDynamic() method is provided: public static class DynamicWrapperExtensions { public static dynamic ToDynamic<T>(this T value) { return new DynamicWrapper<T>(ref value); } } and a ToStatic() method is provided to unwrap the value: public class DynamicWrapper<T> : DynamicObject { public T ToStatic() { return this._value; } } In the above TryGetMember() method, please notice it does not output the member’s value, but output a wrapped member value (that is, memberValue.ToDynamic()). This is very important to make the reflection fluent. Now the code becomes: IEnumerable<Product> results = database.ToDynamic() // Here starts fluent reflection. .Provider.Execute(query.Expression).ReturnValue .ToStatic(); // Unwraps to get the static value. With the help of TryConvert(): public class DynamicWrapper<T> : DynamicObject { public override bool TryConvert(ConvertBinder binder, out object result) { result = this._value; return true; } } ToStatic() can be omitted: IEnumerable<Product> results = database.ToDynamic() .Provider.Execute(query.Expression).ReturnValue; // Automatically converts to expected static value. Take a look at the reflection code at the beginning of this post again. Now it is much much simplified! Special scenarios In 90% of the scenarios ToDynamic() is enough. But there are some special scenarios. Access static members Using extension method ToDynamic() for accessing static members does not make sense. Instead, DynamicWrapper<T> has a parameterless constructor to handle these scenarios: public class DynamicWrapper<T> : DynamicObject { public DynamicWrapper() // For static. { this._type = typeof(T); this._isValueType = this._type.IsValueType; } } The reflection code should be like this: dynamic wrapper = new DynamicWrapper<StaticClass>(); int value = wrapper._value; int result = wrapper.PrivateMethod(); So accessing static member is also simple, and fluent of course. Change instances of value types Value type is much more complex. The main problem is, value type is copied when passing to a method as a parameter. This is why ref keyword is used for the constructor. That is, if a value type instance is passed to DynamicWrapper<T>, the instance itself will be stored in this._value of DynamicWrapper<T>. Without the ref keyword, when this._value is changed, the value type instance itself does not change. Consider FieldInfo.SetValue(). In the value type scenarios, invoking FieldInfo.SetValue(this._value, value) does not change this._value, because it changes the copy of this._value. I searched the Web and found a solution for setting the value of field: internal static class FieldInfoExtensions { internal static void SetValue<T>(this FieldInfo field, ref T obj, object value) { if (typeof(T).IsValueType) { field.SetValueDirect(__makeref(obj), value); // For value type. } else { field.SetValue(obj, value); // For reference type. } } } Here __makeref is a undocumented keyword of C#. But method invocation has problem. This is the source code of TryInvokeMember(): public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { if (binder == null) { throw new ArgumentNullException("binder"); } MethodInfo method = this._type.GetTypeMethod(binder.Name, args) ?? this._type.GetInterfaceMethod(binder.Name, args) ?? this._type.GetBaseMethod(binder.Name, args); if (method != null) { // Oops! // If the returnValue is a struct, it is copied to heap. object resultValue = method.Invoke(this._value, args); // And result is a wrapper of that copied struct. result = new DynamicWrapper<object>(ref resultValue); return true; } result = null; return false; } If the returned value is of value type, it will definitely copied, because MethodInfo.Invoke() does return object. If changing the value of the result, the copied struct is changed instead of the original struct. And so is the property and index accessing. They are both actually method invocation. For less confusion, setting property and index are not allowed on struct. Conclusions The DynamicWrapper<T> provides a simplified solution for reflection programming. It works for normal classes (reference types), accessing both instance and static members. In most of the scenarios, just remember to invoke ToDynamic() method, and access whatever you want: StaticType result = someValue.ToDynamic()._field.Method().Property[index]; In some special scenarios which requires changing the value of a struct (value type), this DynamicWrapper<T> does not work perfectly. Only changing struct’s field value is supported. The source code can be downloaded from here, including a few unit test code.

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  • a class function with if(this==NULL) test got compiled?

    - by James
    I saw this code snippet during our lab and it actually compiles in MSVC2008 and G++. void LinkList< class T ::Insert(T n) { if (this == NULL) // some code here } As far as I know the this must not be null since you cannot call a class functions in c++ if it wasn't instantiated. Is this a valid code? if so what's the reason behind and where it can be useful?

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  • How can i implement the NULL Object Design Pattern in a generic form?

    - by Colour Blend
    Is there a way to implement the null object design pattern in a generic form so that i don't need to implement it for every buisness object. For me, there are two high level classes you'll need for every business class. One for a single record and another for a list. So i think there should be a way to implement the NULL Object design pattern at a high level and not have to implement it for every class. Is there a way and how please?

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