Hello NewsGroup,
I have created a little example with the Join Operator. But I'm a
newbie in LinQ, so I dont know if its my fault.
I have two tables: hotel and guest. In guest is a foreign key to
hotel. Now I want to make a Join in VB:
> Dim HotelJoin = From Hotel In oDb.Hotel Join Guest In oDb.Guest On Hotel.ID
> Equals Guest.HotelID
But it does not work. The HotelJoin.First() function throws an
exception 1010. Does somebody know what I'm doing wrong?
Regards
Mike
PS: I have attached a SQL Script for creating the database and the VB
Function for verifying the error.
########################################################################################
#### This SQL script creates one database (tourist) and two tables
(hotel and guest) in a MySQL DB:
CREATE SCHEMA IF NOT EXISTS `Tourist` DEFAULT CHARACTER SET latin1
COLLATE latin1_german1_ci ;
USE `Tourist`;
-- -----------------------------------------------------
-- Table `Tourist`.`Hotel`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `Tourist`.`Hotel` ;
CREATE TABLE IF NOT EXISTS `Tourist`.`Hotel` (
`ID` INT UNSIGNED NOT NULL AUTO_INCREMENT ,
`HotelName` VARCHAR(45) NOT NULL ,
PRIMARY KEY (`ID`) )
ENGINE = InnoDB
COMMENT = '<double-click to overwrite multiple objects>';
-- -----------------------------------------------------
-- Table `Tourist`.`Guest`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `Tourist`.`Guest` ;
CREATE TABLE IF NOT EXISTS `Tourist`.`Guest` (
`ID` INT UNSIGNED NOT NULL AUTO_INCREMENT ,
`GuestName` VARCHAR(50) NULL ,
`Hotel_ID` INT UNSIGNED NOT NULL ,
PRIMARY KEY (`ID`) ,
INDEX `fk_Gast_Hotel` (`Hotel_ID` ASC) ,
CONSTRAINT `fk_Gast_Hotel`
FOREIGN KEY (`Hotel_ID` )
REFERENCES `Tourist`.`Hotel` (`ID` )
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB
########################################################################################
########################################################################################
#### Try this function to test the join:
Sub Main()
Dim sBogenDbConnInfo As String = "server=127.0.0.1;user id=root;
password=root; database=Tourist"
Dim oDb As TouristLinq.Tourist = New TouristLinq.Tourist(New
MySql.Data.MySqlClient.MySqlConnection(sBogenDbConnInfo))
Dim HotelJoin = From Hotel In oDb.Hotel _
Join Guest In oDb.Guest _
On Hotel.ID Equals Guest.HotelID
' HotelJoin is empty? But I have inserted matching entries in
table hotel and guest?
Dim Row1 = HotelJoin.First() ' Here I get the exception 1010
Dim o = From HotelList In oDb.Hotel ' Here I get my one and only
hotel row
Dim p = From GuestList In oDb.Guest ' In p is the Guest saved. All
ID's are 1, so the values fit.
End Sub
########################################################################################
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