StartWith method in Mark DLinq DynamicQueryExtension class

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Andrus - 22 Jan 2008 23:27 GMT

I tried to create StartsWith extension method for Mark DynamicQueryExtension
class published earlier.

I got compile error shown in comment.

How to fix ?

Andrus.

/// <summary>
/// Returns all items whose property name starts with value, case
insensitive.
///
/// Sample:
/// var q = db.Products.StartsWith( "ProductName", "P" )
///
/// Executes query
/// var q = from p in db.Products
/// where p.ProductName.ToUpper().StartsWith(value.ToUpper(), true,
/// System.Globalization.CultureInfo.CurrentCulture)
/// select p;

/// <param name="propertyName">entity property name, must be string
property</param>

/// <param name="value">value with the property value starts</param>

///
/// </summary>

public static IQueryable<TEntity> StartsWith<TEntity>(this
IQueryable<TEntity> query, string propertyName, string value) {

ParameterExpression param = Expression.Parameter(typeof(TEntity), "p");
// 'System.Linq.Expressions.LambdaExpression' does not contain a
// definition for 'StartsWith'
BinaryExpression testExp = LambdaExpression.StartsWith(
Expression.Property(param, propertyName),
Expression.Constant(value.ToUpper(), typeof(string))
);

return query.Where(Expression.Lambda<Func<TEntity,bool>>(testExp, param));
}

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Nicholas Paldino [.NET/C# MVP] - 23 Jan 2008 03:22 GMT

Andrus,

Well, the error is pretty explicit. You are trying to call the static
StartsWith method on the LambdaExpression class. However, that method
doesn't exist.

Signature

- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard.caspershouse.com

>I tried to create StartsWith extension method for Mark
>DynamicQueryExtension
[quoted text clipped - 40 lines]
> return query.Where(Expression.Lambda<Func<TEntity,bool>>(testExp, param));
> }

Reply to this Message

Andrus - 23 Jan 2008 13:39 GMT

Nicholas,

> Well, the error is pretty explicit. You are trying to call the static
> StartsWith method on the LambdaExpression class. However, that method
> doesn't exist.

Thank you.
Do you have any idea how to fix this code?

I want Dynamic Linq to force generation of parameterized query

ExecuteCommand( "select * FROM Products WHERE %0 ILIKE %1 || '%' ",
columnName, startOfValue );

In this case server uses index if this exists.

Andrus.

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Andrus - 23 Jan 2008 18:24 GMT

> Well, the error is pretty explicit. You are trying to call the static
> StartsWith method on the LambdaExpression class. However, that method
> doesn't exist.

I think I need to create expression

p.&propertyName.StartsWith(&value,
System.StringComparison.CurrentCultureIgnoreCase)

I tried the code below got got runtime error

No method 'StartsWith' on type 'System.String' is compatible with the
supplied arguments.

StartsWith( string, System.StringComparison ) method exists in .NET

How to fix this error ?

public static IQueryable<TEntity> StartsWith<TEntity>(this
IQueryable<TEntity> query, string propertyName, string value) {

ParameterExpression param = Expression.Parameter(typeof(TEntity), "p");

//Error: No method 'StartsWith' on type 'System.String' is compatible with
the supplied arguments.

MethodCallExpression testExp = LambdaExpression.Call(
Expression.Property(param, propertyName),
"StartsWith",
new Type[] { typeof(string), typeof(System.StringComparison) },
new Expression[] { Expression.Constant(value),
Expression.Constant(System.StringComparison.CurrentCultureIgnoreCase) });

return query.Where(Expression.Lambda<Func<TEntity, bool>>(testExp, param));
}

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StartWith method in Mark DLinq DynamicQueryExtension class

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