I am new to linq so please excuse me if I am asking a very basic question:
paymentReceiptViewModel.EntityName = payment.CommitmentPayments.First().Commitment.Entity.GetEntityName();
paymentReceiptViewModel.HofItsId = payment.CommitmentPayments.First().Commitment.Entity.ResponsiblePerson.ItsId;
paymentReceiptViewModel.LocalId = payment.CommitmentPayments.First().Commitment.Entity.LocalEntityId;
paymentReceiptViewModel.EntityAddress = payment.CommitmentPayments.First().Commitment.Entity.Address.ToString();
This code is too repetitive and I am sure there is a better way of writing this.
Thanks in advance for looking this up.
Instead of executing query at each line, get commitment entity once:
var commitment = payment.CommitmentPayments.First().Commitment.Entity;
paymentReceiptViewModel.EntityName = commitment.GetEntityName();
paymentReceiptViewModel.HofItsId = commitment.ResponsiblePerson.ItsId;
paymentReceiptViewModel.LocalId = commitment.LocalEntityId;
paymentReceiptViewModel.EntityAddress = commitment.Address.ToString();
It depends a bit on what you are selecting to, you cannot select from one entity into another in Linq to Entities. If you are using LINQ to SQL and creating the paymentReceiptModel, you can do this.
var paymentReceiptModel = payment.CommitmentPayments.select(x=>new{
EntityName = x.Commitment.Entity.GetEntityName(),
HofItsId = x.Commitment.Entity.ResponsiblePerson.ItsId,
LocalId = x.Commitments.Entity.LocalEntityId,
EntityAddress = x.Commitment.Entity.Address
}).FirstOrDefault();
If you are using an already instantiated paymentReceiptModel and just need to assign properties then you are better looking to the solution by lazyberezovsky.
To get around the limitation in Linq to Entities, if that is what you are using, you could do this
var result = payment.CommitmentPayments.select(x=>x);
var paymentReceiptModel= result.select(x=>new
{
EntityName = x.Commitment.Entity.GetEntityName(),
HofItsId = x.Commitment.Entity.ResponsiblePerson.ItsId,
LocalId = x.Commitments.Entity.LocalEntityId,
EntityAddress = x.Commitment.Entity.Address
}).FirstOrDefault();
This essentially, makes the majority of your query Linq to Objects, only the first line is Linq to Entities
Related
I have an array of string
var searchString = new string[] {"1:PS", "2:PS"};
and a large result string eg;
var largeString = "D9876646|10|1:PS^CD9876647100|11|2:PS"
how do I check if any of the options in searchString exist in the largeString?
I know it can be done via loop quite easily but I am looking for an other way around since I need to append the following as search clause in linq query.
You can use LINQ for it with a simple Any() call, like this:
var hasAny = searchString.Any(sub => largeString.Contains(sub));
However, this is as slow as a foreach loop. You can find the answer faster with a regex constructed from searchString:
var regex = string.Join("|", searchString.Select(Regex.Escape));
var hasAny = Regex.IsMatch(largeString, regex);
Depending on the nature of your LINQ provider (assuming it isn't LINQ to Objects), you may want to add individual tests for each member of searchString. The best way to do this is probably using PredicateBuilder
var sq = PredicateBuilder.New<dbType>();
foreach (var s in searchString)
sq = sq.Or(r => r.largeString.Contains(s));
q = q.Where(sq);
An old question for Linq 2 Entities. I'm just asking it again, in case someone has came up with the solution.
I want to perform query that does this:
UPDATE dbo.Products WHERE Category = 1 SET Category = 5
And I want to do it with Entity Framework 4.3.1.
This is just an example, I have a tons of records I just want 1 column to change value, nothing else. Loading to DbContext with Where(...).Select(...), changing all elements, and then saving with SaveChanges() does not work well for me.
Should I stick with ExecuteCommand and send direct query as it is written above (of course make it reusable) or is there another nice way to do it from Linq 2 Entities / Fluent.
Thanks!
What you are describing isnt actually possible with Entity Framework. You have a few options,
You can write it as a string and execute it via EF with .ExecuteSqlCommand (on the context)
You can use something like Entity Framework Extended (however from what ive seen this doesnt have great performance)
You can update an entity without first fetching it from db like below
using (var context = new DBContext())
{
context.YourEntitySet.Attach(yourExistingEntity);
// Update fields
context.SaveChanges();
}
If you have set-based operations, then SQL is better suited than EF.
So, yes - in this case you should stick with ExecuteCommand.
I don't know if this suits you but you can try creating a stored procedure that will perform the update and then add that procedure to your model as a function import. Then you can perform the update in a single database call:
using(var dc = new YourDataContext())
{
dc.UpdateProductsCategory(1, 5);
}
where UpdateProductsCategory would be the name of the imported stored procedure.
Yes, ExecuteCommand() is definitely the way to do it without fetching all the rows' data and letting ChangeTracker sort it out. Just to provide an example:
Will result in all rows being fetched and an update performed for each row changed:
using (YourDBContext yourDB = new YourDBContext()) {
yourDB.Products.Where(p => p.Category = 1).ToList().ForEach(p => p.Category = 5);
yourDB.SaveChanges();
}
Just a single update:
using (YourDBContext yourDB = new YourDBContext()) {
var sql = "UPDATE dbo.Products WHERE Category = #oldcategory SET Category = #newcategory";
var oldcp = new SqlParameter { ParameterName = "oldcategory", DbType = DbType.Int32, Value = 1 };
var newcp = new SqlParameter { ParameterName = "newcategory", DbType = DbType.Int32, Value = 5 };
yourDB.Database.ExecuteSqlCommand(sql, oldcp, newcp);
}
need help
I have this enum which sets the PayClassNo to Direct and Indirect. I want to use this enum in my LinQ query.
Here's my scratch LinQ query:
var jDef = from jd in context.GetTable<RJVDefinition>()
select new PayrollJVDefinition
{
JVdefNo = jd.JVDefNo,
AccntCode = jd.AccntCode,
AccntDesc = jd.AccntDesc,
PayClass = enum.GetValue(jd.PayClassNo),
IsFixed = jd.IsFixed,
IsEmployee = jd.IsFixed,
IsAR = jd.IsAR,
CreatedByNo = jd.CreatedByNo,
CreatedDate = jd.CreatedDate,
ModifiedByNo = jd.ModifiedByNo,
ModifiedDate = jd.ModifiedDate
};
Need help because I'm not sure if this will work.
You could certainly do the translation in code, similar to your example (using Enum.Parse), but you don't need to. You can use the designer to set the object property type to an enumerated value. See this article for details.
You just need to parse the Enum just use something like
Enum.Parse(jb.PayClassNo, YourEnumType)
I m trying to do something that look very simple but I hit massive difficulties when I want to make that more dynamic.
Expression<Func<TableServiceEntity, bool>> predicate = (e) => e.PartitionKey == "model" && (e.RowKey == "home" || e.RowKey == "shared");
context.CreateQuery<TableServiceEntity>(tableName).Where(predicate);
I would like to pass an array of rowKey instead of having to hard code the predicate.
When I try to build an expression tree I receive a not supported exception I think it doesn't support invoking as part of the expression tree.
Does someone know how to build and expression tree exactly as the predicate to avoid the not supported exception?
Thank you by advance
So, you can build the query dynamically by using something like this (taken from PhluffyFotos sample):
Expression<Func<PhotoTagRow, bool>> search = null;
foreach (var tag in tags)
{
var id = tag.Trim().ToLowerInvariant();
if (String.IsNullOrEmpty(id))
{
continue;
}
Expression<Func<PhotoTagRow, bool>> addendum = t => t.PartitionKey == id;
if (search == null)
{
search = addendum;
}
else
{
search = Expression.Lambda<Func<PhotoTagRow, bool>>(Expression.OrElse(search.Body, addendum.Body), search.Parameters);
}
}
Now, once you have 'search' you can just pass that as the predicate in your Where clause.
However, I want to convince you not to do this. I am answering your question, but telling you that it is a bad idea to do a multiple '|' OR clause in Table storage. The reason is that today at least, these queries cannot be optimized and they cause a full table scan. The performance will be horrendous with any non-trivial amount of data. Furthermore, if you build your predicates dynamically like this you run the risk of blowing the URL limit (keep that in mind).
This code in PhluffyFotos shows how, but it is actually a bad practice (I know, I wrote it). It really should be optimized to run each OR clause separately in parallel. That is how you really should do it. AND clauses are ok, but OR clauses should be parallelized (use PLINQ or TPL) and you should aggregate the results. It will be much faster.
HTH.
I believe what HTH said about this kind of query doing a full table scan is incorrect from the documentation I have read. Azure will perform a PARTITION scan rather than a TABLE scan which is a big difference in performance.
Here is my solution please read also the answer from HTH who pointed out that this is not a best practice.
var parameter = Expression.Parameter(typeof(TableServiceEntity), "e");
var getPartitionKey = typeof(TableServiceEntity).GetProperty("PartitionKey").GetGetMethod();
var getRowKey = typeof(TableServiceEntity).GetProperty("RowKey").GetGetMethod();
var getPartition = Expression.Property(parameter, getPartitionKey);
var getRow = Expression.Property(parameter, getRowKey);
var constPartition = Expression.Constant("model", typeof(string));
var constRow1 = Expression.Constant("home", typeof(string));
var constRow2 = Expression.Constant("shared", typeof(string));
var equalPartition = Expression.Equal(getPartition, constPartition);
var equalRow1 = Expression.Equal(getRow, constRow1);
var equalRow2 = Expression.Equal(getRow, constRow2);
var and = Expression.AndAlso(equalPartition, Expression.OrElse(equalRow1, equalRow2));
return Expression.Lambda<Func<TableServiceEntity, bool>>(and, parameter);
I'm trying to get Entity Framework to select an object and filter its collection at the same time. I have a JobSeries object which has a collection of jobs, what I need to do is select a jobseries by ID and filter all the jobs by SendDate but I can't believe how difficult this simple query is!
This is the basic query which works:
var q = from c in KnowledgeStoreEntities.JobSeries
.Include("Jobs.Company")
.Include("Jobs.Status")
.Include("Category")
.Include("Category1")
where c.Id == jobSeriesId
select c;
Any help would be appreciated, I've been trying to find something in google and what I want to do is here:http://blogs.msdn.com/bethmassi/archive/2009/07/16/filtering-entity-framework-collections-in-master-detail-forms.aspx
It's in VB.NET though and I couldn't convert it to C#.
EDIT: I've tried this now and it doesn't work!:
var q = from c in KnowledgeStoreEntities.JobSeries
.Include("Jobs")
.Include("Jobs.Company")
.Include("Jobs.Status")
.Include("Category")
.Include("Category1")
where (c.Id == jobSeriesId & c.Jobs.Any(J => J.ArtworkId == "13"))
select c;
Thanks
Dan
Include can introduce performance problems. Lazy loading is guaranteed to introduce performance problems. Projection is cheap and easy:
var q = from c in KnowledgeStoreEntities.JobSeries
where c.Id == jobSeriesId
select new
{
SeriesName = c.Name,
Jobs = from j in c.Jobs
where j.SendDate == sendDate
select new
{
Name = j.Name
}
CategoryName = c.Category.Name
};
Obviously, I'm guessing at the names. But note:
Filtering works.
SQL is much simpler.
No untyped strings anywhere.
You always get the data you need, without having to specify it in two places (Include and elsewhere).
No bandwith penalties for retrieving columns you don't need.
Free performance boost in EF 4.
The key is to think in LINQ, rather than in SQL or in materializing entire entities for no good reason as you would with older ORMs.
I've long given up on .Include() and implemented Lazy loading for Entity Framework