This question already has answers here:
LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression
(13 answers)
Closed 2 years ago.
I got this error:
System.NotSupportedException: 'LINQ to Entities does not recognize the
method 'System.String ToString(System.String)'
method, and this method cannot be translated into a store
expression.'
The code is as below:
var search = filter.getFilterValueFor("StartDate", "eq");
query = query.Where(it => it.it.it.ne.newWo.wo.STRT_DT.GetValueOrDefault().ToString("dd/MM/yyyy").Contains(search));
var total = query.Count();
How to solve this error? Thank you.
An IQueryable<...> does not represent a sequence of similar items, it represents the potential to get a sequence of similar items.
To do this, the IQueryable has an Expression and a Provider. The Expression holds the query that must be executed in some generic format. The Provider knows who must execute the query (usually a database management system) and what language is used to communicate with the DBMS (usually SQL).
When you start enumerating, either explicitly, using IQueryable.GetEnumerator(), or at higher level using foreach / ToList() / FirstOrDefault() / Any(), etc, the Expression is sent to the Provider, who will try to translate it into SQL and execute the query. The fetched data is returned as an IEnumerator<...>.
Back to your problem
Your provider does not know method ToString(string). In fact there are several LINQ methods that are not supported by your Provider. See List of Supported and Unsupported LINQ methods (LINQ to entities).
You also use the method String.Contains, which the Provider also will not know. Even if you would solve the ToString(string) problem you would stumble into this similar problem.
What you could do, is transfer the value in its original DateTime format to your local process, and convert it there to a String, and use the Contain. Transferring the data to your local process is done using AsEnumerable. This is preferred above ToList, because AsEnumerable will not fetch much more data than you will use, ToList will fetch everything.
The problem is that you use this construction to filter the fetched data (Where). So if you would use that solution, you will transfer way more data than you would need.
Alas you forgot to mention what you want to query. I think that you want to get all items where the string version of a date "dd/MM/yyyy" contains "2020", or "11": you want all items of a certain year, or all items from November, or maybe the first day of each month.
If that is the case, consider to translate the value of search from string to the year (or month, or date) that you want to fetch, and use DateTime.Year (or month, or Day), to compare.
One final solution: use SQL Like. See class DbFunctions
Next time: don't give us code and say: "this code doesn't do what I want", give us (also) a description of what you do want.
Related
I am trying to convert the following SQL statement to LINQ.
SELECT * FROM History WHERE CONVERT(VARCHAR(50), ActionDate, 112) IN ('20221116');
This ActionDate field contains both date and time and I only want to compare dates in LINQ.
So first I run a simple LINQ query to get all dates from table and then store them in a list so I can pass them to next LINQ for comparison like above. Here's my list. This is just for example otherwise I am actually getting values from database.
var someDates = new List<string>() { "11/16/2022" };
Then I pass it to next LINQ query but it throws error.
db.MyTable.Where(u => someDates.Contains(u.ActionDate.ToShortDateString())).ToList();
Error
LINQ to Entities does not recognize the method 'System.String ToShortDateString()' method and this method cannot be translated into a store expression
If I use AsEnumerable then I get a different error.
db.MyTable.AsEnumerable().Where(u => someDates.Contains(u.ActionDate.ToShortDateString())).ToList();
Error
This function can only be invoked from LINQ to Entities.
How do I fix this issue where I need to pas multiple date values to LINQ to pick only those records?
So with ActionDate being a DateTime data type you could get results from your data table using something along the lines of:
var results = db.MyTable.Where(x=>x.ActionDate.Date == DateTime.Parse(<date_string>).Date);
Results should be a list of entries within the table where the dates match.
You may need to use DateTime.Parse with a Culture format provider in your solution to cope with dd/MM/yyyy and MM/dd/yyyy formats etc.
I save my data in a binary-look string, "100010" ,for example. And I want to check whether it has same value in corresponding place with the other string "100000".
So I try to use "Intersection". In this Condition, the result of intersection will be "100000", and it could be seen as the item I need for my requirement. But how can I use this conception when I query a Entity to Linq statement?
Here is my thought:
var chemicals = db.ChemicalItem.Where(c => c.CategoryNumber.ToCharArray().Intersect(catekey.ToCharArray()).Count()>0);
"CategoryNumber" is my data, and "catekey" is the string for comparing. Both of them are binary-look string(cantain 6 chars). And if the count is not 0,they have '1's in the same index. And I can get the correct query.
Sadly, It didn't work. I always get DbExpressionBinding Error. Can somone tell me What's Wrong? Thanks.
PS:I'm not good at English and post the question here first time, sorry for my bad expression and thank for your reading.
LINQ to Entities is trying to create a SQL query out of your condition, but is not able to do it for the expression you specified.
One way to "fix" the problem would be to do the filtering in code instead of in SQL, but this will impact performance, because all of the records will be retrieved to the client and filtered there. This is how you could do it (notice the added ToList()):
var chemicals = db.ChemicalItem.ToList().Where(c => c.CategoryNumber.ToCharArray().Intersect(catekey.ToCharArray()).Count()>0);
A suggested way would be to do the filtering in SQL, but in this case you will need to write an equivalent stored procedure in SQL which will do the filtering and call that from your EF code. Still such filtering will not be very effective because SQL will not be able to use any indices and will always need to do a table scan.
I recently found out that i cannot call any methods from within a linq query. I am trying to write a query that, on the where clause compares two byte arrays. The value on the database is a GUID of type Raw(32) and it is returned as a byte array. This is the record ID for this table. I need to compare it to another byte array. the second byte array could be converted to a string but since i cannot call methods from within linq i was unable to compare.
I tied a custom "Compare" method, i also wrote an extension method. All received an error indicating "LINQ to Entities does not recognize the method"
Here is the code for what i am trying to do. The where clause causes this error:
LINQ to Entities does not recognize the method 'Boolean SequenceEqual[Byte] (System.Collections.Generic.IEnumerable1[System.Byte], System.Collections.Generic.IEnumerable1[System.Byte])' method, and this method cannot be translated into a store expression."
EPSGEntities dbContex = new EPSGEntities();
byte[] byteArray = ParseHex(ViewState["itemID"].ToString());
var q = (from d in dbContex.EPSG_VSOREJECTS
where d.SDSRECID.SequenceEqual(byteArray)
select d).First();
What version of EntityFramework are you using? On EF6 I am able to simply do the following against a SQL 2012 table with a varbinary column:
var q = dbContext.EPSG_VSOREJECTS.FirstOrDefault(e => e.SDSRECID == byteArray);
Is the SDSRECID property on EPSGEntities of type byte[]?
The alternative here would be to go to straight Sql to get your object. Something like:
dbContext.Database.SqlQuery<EPSG_VSOREJECT>("SELECT TOP 1 *" +
"FROM dbo.EPSGEntities" +
"WHERE SDSRECID = #byteString",
new SqlParameter
{
ParameterName = "byteString",
Value = ViewState["itemID"].ToString(),
}).FirstOrDefault();
Linq to Entities in EF is awesome for most queries, but I sometimes drop into sql when I need to do something unsupported, complex, or just fast. Hope this helps!
I'm not entirely sure this works, but I've found calling .AsEnumerable() on the IQueryable object set lets me apply pretty much any code I wish:
var q = dbContex.EPSG_VSOREJECTS.
.AsEnumerable()
.Where(d => d.SDSRECID.SequenceEqual(byteArray));
Doing so seems to prevent EF from trying to translate the Where() clause into SQL syntax, but I have no real idea what the performance hit would/will be.
This is also using method syntax, since I'm not real familiar with query syntax. HTH.
EDIT:
As some others have noted, you have to be careful with how you add any of the iterative methods (AsEnumerable(), ToList(), etc.) since past that point you are no longer building SQL against your data store. Once you start iterating, EF will execute whatever query has been built up to that point, and from then on you are filtering the result set from the LINQ query.
In this case, I don't know that this can be avoided, unless someone can build the same query as a sproc (which EF can execute on your behalf).
I'm getting the error:
LINQ to Entities does not recognize the method 'Int32 LastIndexOf(System.String)'
method, and this method cannot be translated into a store expression.
When using this code to tell if a person's last name starts with certain characters:
persons = persons.Where(c => c.FullName.IndexOf(" ") > 0 &&
c.FullName.Substring(c.FullName.LastIndexOf(" ")+1).StartsWith(lastNameSearch));
Any clue how to achieve this without using LastIndexOf()? Maybe I have to check for this after I grab results from the database using ToList()?
You are limited by the set of canonical functions that can be translated into an SQL query, so any solution must be achieved with no more than the canonical functions offer.
Luckily, one of the supported functions is the bool Contains(string) instance method. You can rewrite your check as
persons = persons.Where(c => c.FullName.Contains(" " + lastNameSearch));
This is not exactly like your current version (because it will allow people with more than one name to match their second name, while the former won't), but it's pretty close and IMHO can be acceptable.
Of course it would be much better than any of this to keep the last names as a separate column in the database, if that is at all possible.
So, in my last post I was asking how to build a dynamic search filter using LINQ and EF4 (See Here) and finally came up with the solution of building the expression as a string and parse it to an expression using the Dynamic LINQ library.
I that solved the problem. I was able to generate a Expression<Func<TSource, out bool>> and pass it to the Where() method of the DbSet. I am also trying to do this using MySql as a database behind EF4.
The problem came when I tried to apply string operations to integers, like searching a database record which consecutive number starts with 1234.
My initial expression was something like: record.ConsecutiveNumber.ToString().StartsWith("1234"). Sadly, as expected, things were not that easy as EF4 fails to query the DbSet with exception:
"LINQ to Entities does not recognize
the method 'System.String ToString()'
method, and this method cannot be
translated into a store expression."
After some Google search I found that this is a common problem. But C'MON! Is there a way to perform a search function that can search records with a consecutive number starting by "1234"?
How pros implement search features with EF4? This is with a single property filter. What if I wanna add multiple filters? God, my head hurts... :/
Thanks!
EDIT:
Thought #1: What about a stored procedure? What about calling a MySql stored procedure from Linq? Am I aiming way too high?
You can use the SqlFunctions.StringConvert method. It requires a double (or decimal) so you'll have to cast your int ConsecutiveNumber.
Replace:
record.ConsecutiveNumber.ToString().StartsWith("1234")
With:
SqlFunctions.StringConvert((double)record.ConsecutiveNumber).StartsWith("1234")
Have you looked at the Dynamic LinQ Library:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
And for your question
How to use "contains" or "like" in a dynamic linq query?
Previously I have gotten the code for this lib and just taken a look inside, it is pretty easy to follow.
This would be my thought process on getting it to work. Hopefully it points you in the right direction.
According to other posts SqlFunctions.StringConvert((double)record.ConsecutiveNumber) works for Sql Server.
Problem with converting int to string in Linq to entities
And here is relevant information on linq conversions.
Linq int to string
And here is an answer hinting at writing your own sql function for stringconvert
Using a SQL Function in Entity Framework Select
If SqlFunctions.StringConvert doesn't work for you I'd suggest looking at figuring out how to do it in Sql and then writing your own [EdmFunction()] attribute based method.
I haven't got a clue if this will work over Linq to EF or not but presuming that they mapped the Math operations, this might solve your need:
record.ConsecutiveNumber / Math.Pow(10, Math.Truncate(Math.Log10(record.ConsecutiveNumber) - 3)) == 1234
This is basically dividing the number by a power of 10 just big enough to leave the first 4 digits.
I know this is very hacky and inefficient even if it works, but there you go. :)
Any method calls in a LINQ to Entities query that are not explicitly mapped to a canonical function will result in a runtime NotSupportedException exception being thrown.
Check mapping canonical function here:
http://msdn.microsoft.com/en-us/library/bb738681.aspx
In this case, you can use Math function. (I don't think code first can use in product project at that time)