I have a products table which contains thousands of products. I want to update only two columns (price, isAvailable) of this table. So is there is a way to select only those two columns from this table?
This is the code that I am using. But I don't want to select all columns.
var dbModels = await DbContext.Products
.Where(x => x.SellerId == sellerId)
.ToListAsync();
I have tried this
var db = await DbContext.ProductSkuDetail
.Where(x => x.SellerId == sellerId)
.Select(y => new
{
Price = y.Price,
IsAvailable = y.IsAvailable
}).ToListAsync();
But this is read-only. I want to update those columns.
You must include the primary key in the anonymous type:
var models = await context.Products
.Where(p => p.SellerId == sellerId)
.Select(p => new
{
Id = p.Id, // primary key
Price = p.Price,
IsAvailable = p.IsAvailable
})
.ToListAsync();
Then, when you need to save the data back to the database, you need to create entities with the same primary key and attach them to the context.
foreach (var x in models)
{
var product = new Product
{
Id = x.Id,
Price = newPrice, // get new price somehow
IsAvailable = false // get new availability somehow
};
context.Attach(product);
var entry = context.Entry(product);
entry.Property("Price").IsModified = true;
entry.Property("IsAvailable").IsModified = true;
}
await context.SaveChangesAsync();
More info about Attach
Yes, there is a way to specify exactly which columns you want.
No, you can't use that method to update data.
When fetching data using entity framework DbSet<...>, there are two methods: fetch the complete row of the table, or only fetch certain properties of the row.
The first method is used, if you execute the query without using Select. If you do this, the data is copied to the DbContext.ChangeTracker.
Other methods like DbSet.Find and IQueryble.Include will also copy the fetched data to the ChangeTracker.
If you use Select to specify the data that you want to fetch, then the fetched data will not be copied into the ChangeTracker.
When you call DbContext.SaveChanges, the ChangeTracker is used to determine what items are changed or removed and thus need to be updated.
The ChangeTracker keeps the original fetched data, and a copy of it. You get the reference to the copy as the result of your changes. So whenever you change the values of properties of your reference to the copy, they are changed in the copy that is in the ChangeTracker.
When you call SaveChanges, the copy is compared to the original in the ChangeTracker, to detect which properties are changed.
To improve efficiency, if you don't plan to update the fetched data, it is wise to make sure that the fetched data is not in the ChangeTracker.
When using entity framework to fetch data, always use Select and fetch only the properties that you actually plan to use. Only query without Select if you plan to change the fetched data.
Change = update properties, or remove the complete row. Also: only use Find and Include if you plan to update the fetched data.
You want to update the fetched row
Hence you have to fetch the complete row: don't use Select, fetch the complete row.
If you want to fetch the item by primary key, consider to use DbSet.Find. This has the small optimization that if it is already in the ChangeTracker, then the data won't be fetched again.
Consider to write SQL for this
Usually you don't have to update thousands of items on a regular basis. However, if you have to do this often, consider to update using sql:
using (var dbContext = new MyDbContext(...))
{
const string sqlText = #"Update products
SET Price = #Price, IsAvailable = #IsAvailable....
Where SellerId = #SellerId;";
var parameters = new object[]
{
new SqlParameter("#SellerId", sellerId),
new SqlParameter("#Price", newPrice),
new SqlParameter("#IsAvailable", newAvailability),
};
dbContext.DataBase.ExecuteSqlCommand(sqlText, parameters);
}
(You'll have to check the validity of the SQL command in my example. Since I use entity framework, my SQL is a bit rusty.)
By the way: although this method is very efficient, you'll lose the advantages of entity framework: the decoupling of the actual database from the table structure: the names of your tables and columns seep through until this statement.
My advice would be only to use direct SQL for efficiency: if you have to update quite often. Your DbContext hides the internal layout of your database, so make this method part of your DbContext
public void UpdatePrice(int sellerId, bool IsAvailable, decimal newPrice)
{
const string sqlText = ...
var params = ...
this.Database.ExecuteSqlCommand(sqlText, params);
}
Alas, you'll have to call this once per update, there is no SQL command that will update thousands of items with different prices in one SQLcommand
}
You can use the ExecuteSqlCommandAsync Command to write the query which will be executed in your SQL Server.
await dbContext
.Database
.ExecuteSqlCommandAsync("UPDATE Products SET Price = {0}, IsAvailable = {1} WHERE SelleriId = {2}", new object[] { priceValue, isAvailableValue, sellerId });
EF doesn't fit well for batch operations.
It works with objects, not tables, records or fields. If you want to update or delete object(s), you need to read it(them) first. This allows EF change tracker to track changes in field values or the whole object state, and generate appropriate SQL.
For batch operations consider using raw SQL queries, light-weight libraries like Dapper, or third-party packages like Entity Framework Plus.
Related
I have two tables in my database that contain the same columns. TBL one and TBL two which is history table. When I am entering data into TBL 1, I want to move all data from TBL 1 to Tbl 2 (as history data) using EF Core 2.2.
I don't want to write unnecessary loops to make the code ugly.
var MyEntity = new MyEntities();
var TBL1 = MyEntity.TBL1.Find();
var TBL2 = new TBL2();
TBL2.CurrentValues.SetValues(TBL1);
//CurrentValues is not accept in code. Giving me build error
MyEntity.TB2.Add(data2);
MyEntity.TB1.Remove(data1);
MyEntity.SaveChanges();
All I need is copy SQL data from table 1 to table 2 using EF and avoiding loops. Any example with mapper or anything which works will help.
Add a navigation property to your TBL2 model:
public TBL1 TBL1 { get; set; }
Add a projection to your TBL1 model like this:
public static Expression<Func<TBL1, TBL2>> Projection
{
return tbl1 => new TBL2
{
Prop1 = tbl1.Prop1,
Prop2 = tbl1.Prop2,
TBL1 = tbl1,
};
}
And use the projection to have instances of TBL1 and TBL2 like this:
var MyEntity = new MyEntities();
var tbl2 = MyEntity.TBL1.Where(x => x.Id == id).Select(TBL1.Projection).SingleOrDefault();
vat tbl1 = tbl2.TBL1;
MyEntity.TB2.Add(tbl2);
MyEntity.TB1.Remove(tbl1);
MyEntity.SaveChanges();
I assume you don't want to change your table model just for copying data, you want to copy from one table to another, possibly to a different database.
So you could try it with something like this. Use ClearTable to make the target table empty, then copy the items:
void ClearTable<T>(System.Data.Linq.Table<T> tbl, bool submitChanges = true)
where T : class
{
tbl.DeleteAllOnSubmit(tbl);
if (submitChanges) ctxSrc.SubmitChanges();
}
void CopyTable<T>(System.Data.Linq.Table<T> srcTbl,
System.Data.Linq.Table<T> tgtTbl, bool submitChanges = true)
where T : class
{
ClearTable(tgtTbl, submitChanges);
foreach (var element in srcTbl.Select(s => s).ToList())
{
tgtTbl.Append(element);
}
if (submitChanges) ctxTgt.SubmitChanges();
}
Example 1: Copy from one table to another (same database)
CopyTable(ctxSrc.Products1, ctxSrc.Products2);
Example 2: Copy from one database to another
CopyTable(ctxSrc.Products, ctxTgt.Products);
This assumes that you have two database contexts: ctxSrc and ctxTgt and you want to copy from the source context to the target context.
Notes:
The code above deletes items from the target table before copying. Comment the ClearTable call if you just want to append data.
The example doesn't regard dependencies such as foreign key relationshios. You have to add that to the code if required. For example, copying tables in the right order is important. If you have a foreign key pointing to another table you have to copy that table first. Similar rules apply to deletion of rows which contain foreign keys.
If you have many elements, consider to submit more often. This example will hold all elements in memory before it submits. You could achieve this through paging. You can append .Skip(n) and .Take(m) methods for this purpose.
Other than SQL does Entity Framework (Core) not know any true bulk operations. Even tbl.DeleteAllOnSubmit(tbl), which looks like one (it is an integrated method), does internally loop through all elements in order to remove them.
I have a table Estimation which has an column EstimationNo,i am trying to get the max EstimationNo like this-
var result = cont.SalesEstimateCont.Where(x => x.Org_ID == CurrentOrgId);
var estimationMaxNo = result.Any() ? result.Max(x => x.EstimateNo) + 1 : 1;
var DigitalEstimate = new SalesEstimate()
{
EstimateNo=estimationMaxNo;
};
cont.Estimate.Add(DigitalEstimate );
cont.Savechanges();
but the problem is, if same table is saving by different users at same time its saving the same EstimationNo for both users. like- 10,10
Now, how to handle this issue..please give some solution.
Best strategy is to let db engine (I assume that it is SQL Server) handle incrementing of EstimateNo field. This can be done with identity specification which can be added to normal not primary key field also.
ALTER TABLE SalesEstimateCont drop column EstimateNo
go
ALTER TABLE SalesEstimateContadd Add EstimateNo int NOT NULL IDENTITY (1,1)
Please note: if you have existing data or some data should be modified, you may need some extra effort to achieve this (i.e with temp tables and by setting IDENTITY INSERT ON)
I got a simple answer.I just had to use transacationScope class.
and lock the resource table. like this-
using (TransactionScope scope = new TransactionScope())
{
cont.Database.ExecuteSqlCommand("SELECT TOP 1 * FROM Sales__Estimate WITH (TABLOCKX, HOLDLOCK)");
var result = cont.SalesEstimateCont.Where(x => x.Org_ID == CurrentOrgId);
var estimationMaxNo = result.Any() ? result.Max(x => x.EstimateNo) + 1 : 1;
var DigitalEstimate = new SalesEstimate()
{
EstimateNo=estimationMaxNo;
};
cont.Estimate.Add(DigitalEstimate );
cont.Savechanges();
}
If you can make EstimateNo an Identity column, that is the easiest/best way to fix this. If you can change this to a Guid, that would be another easy way to fix this as PK would be unique regardless of the user.
If you can't do either of these and you must take Max() manually, you might want to consider creating another table that stores the next available number there. Then you can create a new SqlCommnand with a Serializable transaction to lock the table, update the # by 1 and select it back. If two update commands hit at the same time, only one update will run and won't let go until that connection with Serializable transaction gets closed. This allows you to select the newly updated number before the other update runs and get the now "unique" next number.
You can OrderByDescending and then Take the the first record
var estimationMaxNo = result.OrderByDescending(x => x.EstimateNo).Take(1);
It can be done in a single command. You need to set the IDENTITY property for primary id
ALTER TABLE SalesEstimateCont ADD Org_ID int NOT NULL IDENTITY (1,1) PRIMARY KEY
I previously asked the question and got answer to Best approach to write query but the problem is that if you have to save this result in a list then there duplication of records. For example
the resultant table of the join given EXAMPLE
See there are duplicate rows. How can you filter them out, and yet save the data of order number?
Of course there may be some ways but I am looking for some great ways
How can we store the data in list and not create duplicate rows in list?
My current code for my tables is
int lastUserId = 0;
sql_cmd = new SqlCommand();
sql_cmd.Connection = sql_con;
sql_cmd.CommandText = "SELECT * FROM AccountsUsers LEFT JOIN Accounts ON AccountsUsers.Id = Accounts.userId ORDER BY AccountsUsers.accFirstName";
SqlDataReader reader = sql_cmd.ExecuteReader();
if (reader.HasRows == true)
{
Users userToAdd = new Users();
while (reader.Read())
{
userToAdd = new Users();
userToAdd.userId = int.Parse(reader["Id"].ToString());
userToAdd.firstName = reader["accFirstName"].ToString();
userToAdd.lastName = reader["accLastName"].ToString();
lastUserId = userToAdd.userId;
Websites domainData = new Websites();
domainData.domainName = reader["accDomainName"].ToString();
domainData.userName = reader["accUserName"].ToString();
domainData.password = reader["accPass"].ToString();
domainData.URL = reader["accDomain"].ToString();
userToAdd.DomainData.Add(domainData);
allUsers.Add(userToAdd);
}
}
For second table I have custom list that will hold the entries of all the data in second table.
The table returned is table having joins and have multiple rows for same
Besides using the Dictionary idea as answered by Antonio Bakula...
If you persist the dictionary of users and call the code in your sample multiple times you should consider that a user account is either new, modifed, or deleted.
The algorithm to use is the following when executing your SQL query:
If row in query result is not in dictionary create and add new user to the dictionary.
If row in query result is in dictionary update the user information.
If dictionary item not in query result delete the user from the dictionary.
I'd also recommend not using SELECT *
Use only the table columns your code needs, this improves the performance of your code, and prevents a potential security breach by returning private user information.
i am not sure why are you not using distinct clause in your sql to fetch unique results. also that will be faster. did you look at using hashtables.
I would put users into Dictonary and check if allready exists, something like this :
Dictionary<int, Users> allUsers = new Dictionary<int, Users>()
and then in Reader while loop :
int userId = int.Parse(reader["Id"].ToString());
Users currUser = allUsers[userId];
if (currUser == null)
{
currUser = new Users();
currUser.userId = userId);
currUser.firstName = reader["accFirstName"].ToString();
currUser.lastName = reader["accLastName"].ToString();
allUsers.Add(userID, currUser);
}
Websites domainData = new Websites();
domainData.domainName = reader["accDomainName"].ToString();
domainData.userName = reader["accUserName"].ToString();
domainData.password = reader["accPass"].ToString();
domainData.URL = reader["accDomain"].ToString();
currUser.DomainData.Add(domainData);
Seems like the root of your problem is in your database table.
When you said duplicate data rows, are you saying you get duplicate entries in the list or you have duplicate data in your table?
Give 2 rows that are duplicate.
Two options:
First, prevent pulling duplicate data from sql by using a distinct clause like:
select distinct from where
Second option as mentioned Antonio, is to check if the list already has it.
First option is recommended unless there are other reasons.
Okay, so I'm new to both EF and LINQ. I have figured out how to INSERT and DELETE but for some reason UPDATE seems to escape my grasp.
Here is a sample of my code:
EntityDB dataBase = new EntityDB();
Customer c = new Customer
{
Name = "Test",
Gender = "Male
};
dataBase.Customers.AddObject(c);
dataBase.SaveChanges();
The above creates and adds a record just fine.
Customer c = (from x in dataBase.Customers
where x.Name == "Test"
selext x).First();
dataBase.Customers.DeleteObject(c);
dataBase.SaveChanges();
The above effectively deletes the specified record.
Now how do I update? I can't seem to find an "UpdateObject()" method on the entity collection.
Just modify one of the returned entities:
Customer c = (from x in dataBase.Customers
where x.Name == "Test"
select x).First();
c.Name = "New Name";
dataBase.SaveChanges();
Note, you can only update an entity (something that extends EntityObject, not something that you have projected using something like select new CustomObject{Name = x.Name}
//for update
(from x in dataBase.Customers
where x.Name == "Test"
select x).ToList().ForEach(xx => xx.Name="New Name");
//for delete
dataBase.Customers.RemoveAll(x=>x.Name=="Name");
They both track your changes to the collection, just call the SaveChanges() method that should update the DB.
In most cases #tster's answer will suffice. However, I had a scenario where I wanted to update a row without first retrieving it.
My situation is this: I've got a table where I want to "lock" a row so that only a single user at a time will be able to edit it in my app. I'm achieving this by saying
update items set status = 'in use', lastuser = #lastuser, lastupdate = #updatetime where ID = #rowtolock and #status = 'free'
The reason being, if I were to simply retrieve the row by ID, change the properties and then save, I could end up with two people accessing the same row simultaneously. This way, I simply send and update claiming this row as mine, then I try to retrieve the row which has the same properties I just updated with. If that row exists, great. If, for some reason it doesn't (someone else's "lock" command got there first), I simply return FALSE from my method.
I do this by using context.Database.ExecuteSqlCommand which accepts a string command and an array of parameters.
Just wanted to add this answer to point out that there will be scenarios in which retrieving a row, updating it, and saving it back to the DB won't suffice and that there are ways of running a straight update statement when necessary.
I have two tables Team_DATA and Driver_PROFILE_DATA in an SQL database. For every driver_profile there can be many teams.
So there's a one-to-many relation on the driver_profile to team_data table. I want to update a team_data foreign key reference in the Driver_profile table of an already existing record to another team_data record that already exists.
I want to do this using entity framework. Here what I want: having a list of teams to select from, finding the record in the team_data table and updating it's FK in the driver_profile appropriately.
So in the code below, the passed parameter is the newly selected team out of the team_data table.
Now I need it to update it FK reference in the Driver_profile table.
Here's what I've got:
UPDATE: Code Updated. It does not save it to database, even if I call savechanges. No errors.
public Driver_PROFILE_DATA GetSelectedTeam(string team)
{
ObjectQuery<Team_DATA> td = raceCtxt.Team_DATA;
ObjectQuery<Driver_PROFILE_DATA> drpr = raceCtxt.Driver_PROFILE_DATA;
var selteam = from t in td where t.Team_Name == team select t;
Team_DATA newteam = new Team_DATA();
newteam = selteam.Select(x => x).First();
// get driver_profile with associated team_data
var data = from a in raceCtxt.Driver_PROFILE_DATA.Include("Team_DATA") select a;
// put it in driver_profile entity
profileData = data.Select(x => x).First();
profileData.Team_DATAReference.Attach(newteam);
return profileData;
}
Entity Framework should give you a nice Association between the two classes, Update the references as you would using POCOs and stay away from the ID values.
Something like:
newTeam.Profile.Teams.Remove(profileData); // separate from old Profile
profileData.Teams.Add(newTeam);
EDIT:
I made a little test, it is sufficient to set the reference to the Parent object:
newTeam.Profile = profileData;