I've got an entity called new_trexmail with a string attribute called new_contextline.
I'm trying to get a list of entities where new_contextlineis in a defined list.
The following code fails with the error : NotSupportedException: Invalid 'where' condition. An entity member is invoking an invalid property or method.
string[] test = new[]{"aaa", "hhh"};
var query = from n in New_trexmailSet
where test.Contains(n.New_contextline)
select n;
I understand why this error is being thrown but I'm wondering if it's possible to do the equiavalent of an IN clause using XRM.
If it is possible then how do I go about getting XRM to execute SELECT * FROM new_trexmail WHERE new_contextline in ('aaa', 'hhh')?
Thanks,
David
Check out the (longer than desired) list of LINQ limitations, particularly the limitation on the where clause:
The left side of the clause must be an attribute name and the right
side of the clause must be a value. You cannot set the left side to a
constant. Both the sides of the clause cannot be constants. Supports
the String functions Contains, StartsWith, EndsWith, and Equals.
So since test isn't a CRM attribute, you can't call Contains on it. However, one way around this is to use "Dynamic Linq" as developed by ScottGu and as demonstrated below:
//must include the below using statements
//using System.Linq;
//using System.Linq.Dynamic;
var trexmailSet = New_trexmailSet;
string[] test = new[] { "aaa", "hhh" };
string whereClause = "";
foreach (string name in test)
{
whereClause += string.Format("new_contextline = \"{0}\" OR ", name);
}
trexmailSet = trexmailSet.Where(whereClause.Substring(0, whereClause.Length - 4));
var query = from n in trexmailSet
select n;
Related
I have some errors using Linq on DataTable and I couldn't figure it out how to solve it. I have to admit that i am pretty new to Linq and I searched the forum and Internet and couldn't figure it out. hope you can help.
I have a DataTable called campaign with three columns: ID (int), Product (string), Channel (string). The DataTable is already filled with data. I am trying to select a subset of the campaign records which satisfied the conditions selected by the end user. For example, the user want to list only if the Product is either 'EWH' or 'HEC'. The selection criteria is dynaically determined by the end user.
I have the following C# code:
private void btnClick()
{
IEnumerable<DataRow> query =
from zz in campaign.AsEnumerable()
orderby zz.Field<string>("ID")
select zz;
string whereClause = "zz.Field<string>(\"Product\") in ('EWH','HEC')";
query = query.Where(whereClause);
DataTable sublist = query.CopyToDataTable<DataRow>();
}
But it gives me an error on line: query = query.Where(whereClause), saying
No property or field 'zz' exists in type 'DataRow'".
If I changed to:
string whereClause = "Product in ('EWH','HEC')"; it will say:
No property or field 'Product' exists in type 'DataRow'
Can anyone help me on how to solve this problem? I feel it could be a pretty simple syntax change, but I just don't know at this time.
First, this line has an error
orderby zz.Field<string>("ID")
because as you said, your ID column is of type int.
Second, you need to learn LINQ query syntax. Forget about strings, the same way you used from, orderby, select in the query, you can also use where and many other operators. Also you'll need to learn the equivalent LINQ constructs for SQL-ish things, like for instance IN (...) is mapped to Enumerable.Contains etc.
With all that being said, here is your query
var productFilter = new[] { "EWH", "HEC" };
var query =
from zz in campaign.AsEnumerable()
where productFilter.Contains(zz.Field<string>("Product"))
orderby zz.Field<int>("ID")
select zz;
Update As per your comment, if you want to make this dynamic, then you need to switch to lambda syntax. Multiple and criteria can be composed by chaining multiple Where clauses like this
List<string> productFilter = ...; // coming from outside
List<string> channelFilter = ...; // coming from outside
var query = campaign.AsEnumerable();
// Apply filters if needed
if (productFilter != null && productFilter.Count > 0)
query = query.Where(zz => productFilter.Contains(zz.Field<string>("Product")));
if (channelFilter != null && channelFilter.Count > 0)
query = query.Where(zz => channelFilter.Contains(zz.Field<string>("Channel")));
// Once finished with filtering, do the ordering
query = query.OrderBy(zz => zz.Field<int>("ID"));
I am trying to programmatically generate an expression tree (that will eventually get used in Linq-to-entity framework).
I can get the query to work just fine with one exception - it does not parametrize the query - which I want for Sql Server query plan reuse.
I read that in order for the generated sql to be parametrized, the expression needs to compare based on a variable. However, I cannot figure out how to assign the value to the variable in the expression tree. If I just use Expression.Constantit works (but is not parametrized).
So basically:
public Expression<Func<T, bool>> FooEquals<T>(
Expression<Func<T, int>> propertyExpression, int value)
{
ParameterExpression param = propertyExpression.Parameters.Single();
int targetValueForEqualityComparison = 9;
//There's some "special sauce" here which is why I don't
//use propertyExpression directly
var body = Expression.Property(param, GetPropertyName(propertyExpression));
//If I just use Expression.Constant, it works, but doesn't parametrize.
//var equalExpression = ParameterExpression.Equal(body,
// Expression.Constant(targetValueForEqualityComparison, typeof(int)));
var variable = Expression
.Variable(typeof(int), "targetValueForEqualityComparison");
var assigned = Expression.Assign(variable,
Expression.Constant(targetValueForEqualityComparison, typeof(int)));
//throws InvalidOperaitonException: "The parameter was not bound in the
//specified Linq to Entities query expression
var equalExpression = ParameterExpression.Equal(body, variable);
//throws NotSupportedException: "Unknown LINQ expression of type 'Assign'.
var equalExpression = ParameterExpression.Equal(body, assigned);
return Expression.Lambda<Func<T, bool>>(equalExpression, param);
}
How do I properly bind a value to the variable expression so that Linq-to-EntityFramework will parametrize the query?
I went ahead and tried it out because I was curious. The following seem to result in identical SQL, at least when used with Linq-to-SQL (which LINQPad does more readily than EF). I'd imagine it should work just the same with EF though.
Seems like a pretty convoluted way to just pass an integer in, but because this is what the compiler generates for a plain lambda function, I guess this is what the SQL generator looks for.
// Given this class, which is equivalent to the compiler-generated class
class Holder {
public int AnInteger;
}
int id = 1;
// You get the same SQL with a plain lambda function
var query = db.Items.Where(i => i.Id == id);
// or with a handwritten expression:
var arg = Expression.Parameter(typeof(Item), "i");
var paramHolder = new Holder { AnInteger = id };
// essentially, (i) => i.Id == paramHolder.AnInteger
var lambda = Expression.Lambda<Func<Item, bool>>(
Expression.Equal(
Expression.Property(arg, "Id"),
Expression.Field(
Expression.Constant(paramHolder), "AnInteger")),
arg);
// the SQL this translates to is equivalent to that of the first query
var query2 = db.Items.Where(lambda);
I've got a situation where I need to use a custom expression in a LINQ to Entities query (because I want to have custom logic that L2E wouldn't otherwise understand:
var query = db.MyTable.Where(MyPredicateExpression)
But I'd rather use query comprehension syntax:
var query = from x in db.MyTable where [x matches the predicate of MyPredicateExpression]
I know this is possible, because L2E supports it in other places:
var query = from x in db.MyTable where x.Length > 10
How do they make that work?
Edit: I'm using devart's LinqConnect for Oracle, which may behave somewhat differently than Microsoft L2E.
Entity Framework and LINQ to SQL do not support this scenario, because the translation of MyPredicateExpression should be added to expression tree translator.
I recommend you to create a stored function performing the predicate check and add this function to DataContext. You will be able to use a query like the following in this case:
var query = from x in db.MyTable where context.MyPredicateFunction(x.Field) select x;
Update. Here is the updated query that takes into account your comments:
int[] values = new int[] { 1, 2, 3 };
var query = from x in db.MyTable where values.Contains(x.AuditState) select x;
Update 2. You can add a Queryable property to your context that will be obtaining the necessary set of MyTable objects as shown in the following example:
public partial class MyDataContext {
IQueryable<MyTable> GetSpecialTables {
get {
int[] values = new int[] { 1, 2, 3 };
return this.MyTables.Where(x => values.Contains(x.AuditState));
}
}
}
Replace MyDataContext with the actual name of your context.
If I understand the problem correctly, you can either use an extension method OR call a function that returns a bool.
I'm very new to Linq, I can find multi-line data reading examples everywhere (by using foreach()), but what is the correct way of reading a single line of data? Like a classic Product Detail page.
Below is what I tried:
var q = from c in db.Products
where c.ProductId == ProductId
select new { c.ProductName, c.ProductDescription, c.ProductPrice, c.ProductDate };
string strProductName = q.First().ProductName.ToString();
string strProductDescription = q.First().ProductDescription.ToString();
string strProductPrice = q.First().ProductPrice.ToString();
string strProductDate = q.First().ProductDate.ToString();
The code looks good to me, but when I see the actual SQL expressions generated by using SQL Profiler, it makes me scared! The program executed four Sql expressions and they are exactly the same!
Because I'm reading four columns from a single line. I think I must did something wrong, so I was wondering what is the right way of doing this?
Thanks!
Using the First() extension method would throw the System.InvalidOperationException when no element in a sequence satisfies a specified condition.
If you use the FirstOrDefault() extension method, you can test against the returned object to see if it's null or not.
FirstOrDefault returns the first element of a sequence, or a default value if the sequence contains no elements; in this case the default value of a Product should be null. Attempting to access the properties on this null object will throw ArgumentNullException
var q = (from c in db.Products
where c.ProductId == ProductId
select new { c.ProductName, c.ProductDescription, c.ProductPrice, c.ProductDate }).FirstOrDefault();
if (q != null)
{
string strProductName = q.ProductName;
string strProductDescription = q.ProductDescription;
string strProductPrice = q.ProductPrice;
string strProductDate = q.ProductDate;
}
Also, you shouldn't have to cast each Property ToString() if you're object model is setup correctly. ProductName, ProductDescription, etc.. should already be a string.
The reason you're getting 4 separate sql queries, is because each time you call q.First().<PropertyHere> linq is generating a new Query.
var q = (from c in db.Products
where c.ProductId == ProductId
select new { c.ProductName, c.ProductDescription, c.ProductPrice, c.ProductDate }
).First ();
string strProductName = q.ProductName.ToString();
string strProductDescription = q.ProductDescription.ToString();
string strProductPrice = q.ProductPrice.ToString();
string strProductDate = q.ProductDate.ToString();
I have a combo box in Silverlight. It has a collection of values built out of the properties of one of my LINQ-to-SQL objects (ie Name, Address, Age, etc...). I would like to filter my results based off the value selected in a combo box.
Example: Say I want everyone with a last name "Smith". I'd select 'Last Name' from the drop down list and enter smith into a textbox control. Normally I would write a LINQ query similar to...
var query = from p in collection where p.LastName == textbox.Text select p;
Is it possible to decide the property dynamically, maybe using Reflection? Something like
var query = from p in collection where p.(DropDownValue) == textbox.Text select p;
Assuming:
public class Person
{
public string LastName { get; set; }
}
IQueryable<Person> collection;
your query:
var query =
from p in collection
where p.LastName == textBox.Text
select p;
means the same as:
var query = collection.Where(p => p.LastName == textBox.Text);
which the compiler translates from an extension method to:
var query = Queryable.Where(collection, p => p.LastName == textBox.Text);
The second parameter of Queryable.Where is an Expression<Func<Person, bool>>. The compiler understands the Expression<> type and generates code to build an expression tree representing the lambda:
using System.Linq.Expressions;
var query = Queryable.Where(
collection,
Expression.Lambda<Func<Person, bool>>(
Expression.Equal(
Expression.MakeMemberAccess(
Expression.Parameter(typeof(Person), "p"),
typeof(Person).GetProperty("LastName")),
Expression.MakeMemberAccess(
Expression.Constant(textBox),
typeof(TextBox).GetProperty("Text"))),
Expression.Parameter(typeof(Person), "p"));
That is what the query syntax means.
You are free to call these methods yourself. To change the compared property, replace this:
typeof(Person).GetProperty("LastName")
with:
typeof(Person).GetProperty(dropDown.SelectedValue);
Scott Guthrie has a short series on dyamically built LINQ to SQL queries:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
That's the easy way...then there's another way that's a bit more involved:
http://www.albahari.com/nutshell/predicatebuilder.aspx
You can also use the library I created: http://tomasp.net/blog/dynamic-linq-queries.aspx. You would store the properties in ComboBox as lambda expressions and then just write:
var f = (Expression<Func<Product, string>>)comboBox.SelectedValue;
var query =
from p in collection
where f.Expand(textBox.Text)
select p;