I'm working on a school project in ASP.NET MVC 5. The project is about creating a social network. After the user logs in, he will see all public posts on his newsfeed.
I am having issues, though, in showing the public posts' data from the database.
This is the script of the database :
create table Utilizador(
id_utilizador integer not null identity(1,1),
nome varchar(50) not null,
apelido varchar(50) not null,
username varchar(15) not null unique,
pass varchar(50) not null,
email varchar(50) not null unique,
sexo char(1) not null CHECK (sexo IN('M', 'F')),
país varchar(50) not null,
imagem_perfil varchar(50) not null,
data_nascimento date not null,
estado int not null default 2, --0->Bloqueado 1-Activo, 2-por activar
primary key (id_utilizador),
check (email LIKE '%#%.%')
)
create table Post(
id_post integer not null identity(1,1),
texto varchar(400) not null,
primary key(id_post)
)
create table Publish_Post(
id_post integer not null,
id_utilizador integer not null,
data timestamp not null,
primary key(id_post),
foreign key(id_post) references Post(id_post),
foreign key(id_utilizador) references Utilizador(id_utilizador)
)
create table Privacy(
id_privacidade integer not null identity(1,1), --> 1 public, 2 private
nome varchar(50) not null,
primary key(id_privacidade)
)
create table Have_Privacy(
id_post integer not null,
id_privacidade integer not null,
primary key(id_post),
foreign key(id_post) references Post(id_post),
foreign key(id_privacidade) references Privacidade(id_privacidade)
)
Let me explain why I create the database the way I do:
The user creates and publishes some posts that have will have a privacy value (1 or 2). After the user logs in, all public posts(1) should appear on his newsfeed.
So far I have this LINQ query in C#:
var id_posts = from p in db.Posts
select p.texto;
ViewBag.Posts = id_posts;
Can someone help me?
Thanks in advance :)
Just do this
var id_posts = from p in db.Posts
join hp in db.Have_Privacy on p.id_post equals hp.id_post
join prv in db.Privacy on hp.id_privacidade equals prv.id_privacidade
where prv.nome = 'Private'
select p.texto;
Tell how it goes
Why not just add a field in Post called isprivate with boolean type of BIT that determines if it's private or not and then use query for provided data with where clause:
var id_posts = from p in db.Posts
where isprivate == false
select p.texto;
If you want to have more than 2 types of privacy and just stick with DB schema you provided, you can go with a JOIN:
If id decides it is private:
var id_posts = from p in db.Posts
join hp in db.Have_Privacy on p.id_post equals hp.id_post
where hp.id_privacidade = 1
select p.texto;
If name decides it is private:
var id_posts = from p in db.Posts
join hp in db.Have_Privacy on p.id_post equals hp.id_post
join prv in db.Privacy on hp.id_privacidade equals prv.id_privacidade
where prv.nome = 'Private'
select p.texto;
Also please note that naming tables in one language and columns in other is considered as bad design. It's hard for others (in this example me) to read it, even if I know what it should mean.
Two last queries use your schema with no changes implemented.
Related
On a project where we have SQL tables called Products and Conditions, we want to determine which product belongs to which most matching condition, because a product can belong to multiple conditions.
Is there a way to do this in C# or SQL?
Below you can find a shorted version of the tables with the properties that we want to match on:
CREATE TABLE Products
(
[Id] INT NOT NULL PRIMARY KEY IDENTITY(1,1),
[Property1] SMALLINT NULL,
[Property2] SMALLINT NULL,
[Property3] NVARCHAR(20) NULL,
[Property4] NVARCHAR(20) NULL
)
CREATE TABLE Conditions
(
[Id] INT NOT NULL PRIMARY KEY IDENTITY(1,1),
[Property1] SMALLINT NULL,
[Property2] SMALLINT NULL,
[Property3] NVARCHAR(20) NULL,
[Property4] NVARCHAR(20) NULL
)
As a result we want for each product the conditions and sorted by most matching score based on the 4 properties.
Because we have 4 properties, the resulting score could be 0 / 25 / 50 / 75 / 100.
In sql you can join the two tables on matching properties and use iif method to compute the total score and order the results by the total score like below :
Select * from (
Select p.*, c.*,
iif([Property1] = p.[Property1],25,0) +
iif([Property2] = p.[Property2],25,0) +
iif([Property3] = p.[Property3],25,0) +
iif([Property4] = p.[Property4],25,0) [TotalScore]
from Products p inner join Conditions c
on c.[Property1] = p.[Property1] or
c.[Property2] = p.[Property2] or
c.[Property3] = p.[Property3] or
c.[Property4] = p.[Property4]) q
order by TotalScore desc
Fairly new to LINQ and am trying to figure out how to write a particular query. I have a database where each CHAIN consists of one or more ORDERS and each ORDER consists of one or more PARTIALS. The database looks like this:
CREATE TABLE Chain
(
ID int NOT NULL PRIMARY KEY CLUSTERED IDENTITY(1,1),
Ticker nvarchar(6) NOT NULL,
Company nvarchar(128) NOT NULL
)
GO
CREATE TABLE [Order]
(
ID int NOT NULL PRIMARY KEY CLUSTERED IDENTITY(1,1),
Chart varbinary(max) NULL,
-- Relationships
Chain int NOT NULL
)
GO
ALTER TABLE dbo.[Order] ADD CONSTRAINT FK_Order_Chain
FOREIGN KEY (Chain) REFERENCES dbo.Chain ON DELETE CASCADE
GO
CREATE TABLE Partial
(
ID int NOT NULL PRIMARY KEY CLUSTERED IDENTITY(1,1),
Date date NOT NULL,
Quantity int NOT NULL,
Price money NOT NULL,
Commission money NOT NULL,
-- Relationships
[Order] int NOT NULL
)
GO
ALTER TABLE dbo.Partial ADD CONSTRAINT FK_Partial_Order
FOREIGN KEY ([Order]) REFERENCES dbo.[Order] ON DELETE CASCADE
I want to retrieve the chains, ordered by the earliest date among all the partials of all the orders for each particular chain. In T-SQL I would write the query as this:
SELECT p.DATE, c.*
FROM CHAIN c
CROSS APPLY
(
SELECT DATE = MIN(p.Date)
FROM PARTIAL p
JOIN [ORDER] o
ON p.[ORDER] = o.ID
WHERE o.CHAIN = c.ID
) AS p
ORDER BY p.DATE ASC
I have an Entity Framework context that contains a DbSet<Chain>, a DbSet<Order>, and a DbSet<Partial>. How do I finish this statement to get the result I want?:
IEnumerable<Chain> chains = db.Chains
.Include(c => c.Orders.Select(o => o.Partials))
.[WHAT NOW?]
Thank you!
.[WHAT NOW?]
.OrderBy(c => c.Orders.SelectMany(o => o.Partials).Min(p => p.Date))
Here c.Orders does join Chain to Order, while o.SelectMany(o => o.Partials) does join Order to Partial. Once you have access to Partial records, you can use any aggregate function, like Min(p => p.Date) in your case.
So i have a bit of a problem, on my ASP.Net website i want it to show all the rooms which are currently available and not in use. When i say not in use i mean at present there is no one reserved to that room, so the systemdate is not between any values of the checkin and checkoutdate.
Part of my schema:
CREATE TABLE "Rooms"(
RoomNo int NOT NULL,
RoomType nvarchar(20) NULL,
PricePerNight money NULL,
MaximumOccupancy int NULL,
NoOfBeds int NULL,
NoOfBathrooms int NULL,
Entertainment bit NULL,
RoomService bit NULL,
Gym bit NULL,
CONSTRAINT PK_Rooms PRIMARY KEY(RoomNo)
)
CREATE TABLE "Reservation"(
ReservationID int IDENTITY (1,1) NOT NULL,
CustomerID int NOT NULL,
RoomNo int NOT NULL,
CheckInDate date NOT NULL,
CheckOutDate date NOT NULL,
NoOfDays int NOT NULL,
CONSTRAINT PK_Reservation PRIMARY KEY(ReservationID),
CONSTRAINT FK_Reservation_Customers_CustID FOREIGN KEY(CustomerID)
REFERENCES dbo.Customers(CustomerID),
CONSTRAINT FK_Reservation_Rooms_RoomNo FOREIGN KEY(RoomNo)
REFERENCES dbo.Rooms(RoomNo)
)
So heres my idea, im assuming im going to need an sql query which goes something like this:
Select All FROM Rooms Where &CheckInDate != "Select CheckIndate From
Reservation" AND &CheckOutDate != "Select CheckOutDate From
Reservation".
But this has some flaws in it.
Can someone please tell me how i can do this, how i can make my Sue-do-code (lets call it) more viable, as i'm not sure if something like that will work, and if necessarily suggest improvements i could make to my schema.
TLDR; i need a query where someone enters a checkindate and checkoutdate and it returns all the rooms which are available.
Try this..
SELECT *
FROM Rooms
WHERE NOT EXISTS
(SELECT *
FROM Room r, Reservation rs
WHERE r.RoomNo = rs.RoomNo AND GETDATE() BETWEEN rs.CheckInDate AND rs.CheckOutDate)
This is what i wanted.
SELECT dbo.Rooms.RoomNo
FROM dbo.Rooms JOIN dbo.Reservation
ON (dbo.Rooms.RoomNo = dbo.Reservation.RoomNo)
WHERE '2012-01-01' NOT BETWEEN dbo.Reservation.CheckInDate AND dbo.Reservation.CheckOutDate
AND '2012-01-05' NOT BETWEEN dbo.Reservation.CheckInDate AND dbo.Reservation.CheckOutDate;
Took time but i got it in the end. the where statement initial date can be replaced with &Date.
Using role based permissions, and say each row in a table represents an entity e.g. the Products table, each row represents a Product entity.
How could you provide Product level security based on roles?
e.g. the Sales group has access to Products with ID's 1,234,432,532,34
Multiple roles can be given permissions on any given product.
The goal is to provide an effecient database call for a query like:
var products = ProductDao.GetProductsByRole(234); // roleID = 234
Many-to-Many relations are stored in a separate table:
create table Products(
ProductId int not null identity (1,1),
Name nvarchar(256) not null,
Description nvarchar(max),
constraint PK_Products primary key (ProductId),
constraint UNQ_Products_Name unique (Name));
create table Roles(
RoleId int not null identity (1,1),
Name nvarchar(256) not null,
Description nvarchar(max),
constraint PK_Roles primary key (RoleId),
constraint UNQ_Roles_Name unique (Name));
go
create table ProductRolePermissions (
ProductId int not null,
RoleId int not null,
constraint FK_ProductRolePermissions_Products
foreign key (ProductId)
references Products(ProductId),
constraint FK_ProductRolePermissions_roles
foreign key (RoleId)
references Roles(RoleId));
go
create unique clustered index CDX_ProductRolePermissions
on ProductRolePermissions (RoleId, ProductId);
create unique nonclustered index NDX_ProductRolePermissions
on ProductRolePermissions (ProductId, RoleId);
go
create function dbo.GetProductsByRole( #roleId int)
returns table
with schemabinding
as return (
select ProductId
from dbo.ProductRolePermissions
where RoleId = #roleId);
go
insert into Products (Name)
values ('P1'), ('P2'), ('P3'), ('P4');
insert into Roles (Name)
values ('G1'), ('G2');
insert into ProductRolePermissions (ProductId, RoleId)
values (1,1), (3,1), (2,2), (3,2);
go
select 'Products permitted for G1', p.*
from dbo.GetProductsByRole(1) r
join Products p on r.ProductId = p.ProductId;
select 'Products permitted for G2', p.*
from dbo.GetProductsByRole(2) r
join Products p on r.ProductId = p.ProductId;
Things get a little more complicated if you want to follow the classical grant/deny/revoke permission model for read/write/full access with multiple role memberships.
I have a MSSQL 2005 table:
[Companies](
[CompanyID] [int] IDENTITY(1,1) NOT NULL,
[Title] [nvarchar](128),
[Description] [nvarchar](256),
[Keywords] [nvarchar](256)
)
I want to generate a tag cloud for this companies. But I've saved all keywords in one column separated by commas. Any suggestions for how to generate tag cloud by most used keywords. There could be millions of companies approx ten keywords per company.
Thank you.
Step 1: separate the keywords into a proper relation (table).
CREATE TABLE Keywords (KeywordID int IDENTITY(1,1) NOT NULL
, Keyword NVARCHAR(256)
, constraint KeywordsPK primary key (KeywordID)
, constraint KeywordsUnique unique (Keyword));
Step 2: Map the many-to-many relation between companies and tags into a separate table, like all many-to-many relations:
CREATE TABLE CompanyKeywords (
CompanyID int not null
, KeywordID int not null
, constraint CompanyKeywords primary key (KeywordID, CompanyID)
, constraint CompanyKeyword_FK_Companies
foreign key (CompanyID)
references Companies(CompanyID)
, constraint CompanyKeyword_FK_Keywords
foreign key (KeywordID)
references Keywords (KeywordID));
Step 3: Use a simple GROUP BY query to generate the 'cloud' (by example taking the 'cloud' to mean the most common 100 tags):
with cte as (
SELECT TOP 100 KeywordID, count(*) as Count
FROM CompanyKeywords
group by KeywordID
order by count(*) desc)
select k.Keyword, c.Count
from cte c
join Keyword k on c.KeywordID = k.KeywordID;
Step 4: cache the result as it changes seldom and it computes expensively.
I'd much rather see your design normalized as suggested by Remus, but if you're at a point where you can't change your design...
You can use a parsing function (the example I'll use is taken from here), to parse your keywords and count them.
CREATE FUNCTION [dbo].[fnParseStringTSQL] (#string NVARCHAR(MAX),#separator NCHAR(1))
RETURNS #parsedString TABLE (string NVARCHAR(MAX))
AS
BEGIN
DECLARE #position int
SET #position = 1
SET #string = #string + #separator
WHILE charindex(#separator,#string,#position) <> 0
BEGIN
INSERT into #parsedString
SELECT substring(#string, #position, charindex(#separator,#string,#position) - #position)
SET #position = charindex(#separator,#string,#position) + 1
END
RETURN
END
go
create table MyTest (
id int identity,
keywords nvarchar(256)
)
insert into MyTest
(keywords)
select 'sql server,oracle,db2'
union
select 'sql server,oracle'
union
select 'sql server'
select k.string, COUNT(*) as count
from MyTest mt
cross apply dbo.fnParseStringTSQL(mt.keywords,',') k
group by k.string
order by count desc
drop function dbo.fnParseStringTSQL
drop table MyTest
Both Remus and Joe are correct but yes as what Joe said if you dont have a choice then you have to live with it. I think I can offer you an easy solution by using an XML Data Type. You can already easily view the parsed column by doing this query
WITH myCommonTblExp AS (
SELECT CompanyID,
CAST('<I>' + REPLACE(Keywords, ',', '</I><I>') + '</I>' AS XML) AS Keywords
FROM Companies
)
SELECT CompanyID, RTRIM(LTRIM(ExtractedCompanyCode.X.value('.', 'VARCHAR(256)'))) AS Keywords
FROM myCommonTblExp
CROSS APPLY Keywords.nodes('//I') ExtractedCompanyCode(X)
now knowing that you can do that, all you have to do is to group them and count, but you cannot group XML methods so my suggestion is create a view of the query above
CREATE VIEW [dbo].[DissectedKeywords]
AS
WITH myCommonTblExp AS (
SELECT
CAST('<I>' + REPLACE(Keywords, ',', '</I><I>') + '</I>' AS XML) AS Keywords
FROM Companies
)
SELECT RTRIM(LTRIM(ExtractedCompanyCode.X.value('.', 'VARCHAR(256)'))) AS Keywords
FROM myCommonTblExp
CROSS APPLY Keywords.nodes('//I') ExtractedCompanyCode(X)
GO
and perform your count on that view
SELECT Keywords, COUNT(*) AS KeyWordCount FROM DissectedKeywords
GROUP BY Keywords
ORDER BY Keywords
Anyways here is the full article -->http://anyrest.wordpress.com/2010/08/13/converting-parsing-delimited-string-column-in-sql-to-rows/