[英]How linq-to-nhibernate between 2 lists by StartsWith
我需要通過NHibernate 4運行此查詢:
var filterList = new List<string> { "1" , "2" } ;
var q = SessionInstance.Query<Book>()
.Where(x => filterList.Any(s => s.StartsWith(x.Code)));
var list = q.ToList();
但是此消息有例外: Specified method is not supported.
堆棧跟蹤 :
at NHibernate.Hql.Ast.ANTLR.PolymorphicQuerySourceDetector.GetClassName(IASTNode querySource)
at NHibernate.Hql.Ast.ANTLR.PolymorphicQuerySourceDetector.Process(IASTNode tree)
at NHibernate.Hql.Ast.ANTLR.AstPolymorphicProcessor.Process()
at NHibernate.Hql.Ast.ANTLR.ASTQueryTranslatorFactory.CreateQueryTranslators(IASTNode ast, String queryIdentifier, String collectionRole, Boolean shallow, IDictionary`2 filters, ISessionFactoryImplementor factory)
at NHibernate.Hql.Ast.ANTLR.ASTQueryTranslatorFactory.CreateQueryTranslators(IQueryExpression queryExpression, String collectionRole, Boolean shallow, IDictionary`2 filters, ISessionFactoryImplementor factory)
at NHibernate.Engine.Query.QueryPlanCache.GetHQLQueryPlan(IQueryExpression queryExpression, Boolean shallow, IDictionary`2 enabledFilters)
at NHibernate.Impl.AbstractSessionImpl.GetHQLQueryPlan(IQueryExpression queryExpression, Boolean shallow)
at NHibernate.Impl.AbstractSessionImpl.CreateQuery(IQueryExpression queryExpression)
at NHibernate.Linq.DefaultQueryProvider.PrepareQuery(Expression expression, IQuery& query, NhLinqExpression& nhQuery)
at NHibernate.Linq.DefaultQueryProvider.Execute(Expression expression)
at NHibernate.Linq.DefaultQueryProvider.Execute[TResult](Expression expression)
at Remotion.Linq.QueryableBase`1.GetEnumerator()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
這沒有實現,但是我們可以將WHERE 條件轉換為OR表達式:
var q = SessionInstance
.Query<Book>()
//.Where(x => filterList.Any(s => s.StartsWith(x.Code)))
.Where(x => x.Code.StartsWith("1")
|| x.Code.StartsWith("2")
)
;
顯然,這不是動態的。 我們必須命名所有 OR語句,我們不能使用filterList
...除非我們尋求LinqKit
幫助
並創建一種自動化的方法。 我們將需要這些using語句:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using LinqKit;
namespace MyNamespace
{
public static partial class Ext
{
...
擴展本身:
public static Expression<Func<T, bool>> AnyStarts<T>(
this IList<string> startsWithValues, Expression<Func<T, string>> property)
{
var nothingToDo = startsWithValues == null
|| startsWithValues.Count == 0
|| property == null;
// nothing to process here, return null
if (nothingToDo)
{
return null;
}
// first value ...
string firstValue = startsWithValues.First();
Expression<Func<T, bool>> predicate =
x => property.Invoke(x).StartsWith(firstValue);
Expression<Func<T, bool>> result = predicate.Expand();
if (startsWithValues.Count == 1)
{
// first value is enough
return result;
}
// let's append Or if there are many string values
for (int index = 1; index < startsWithValues.Count; index++)
{
string nextValue = startsWithValues[index];
predicate = x => result.Invoke(x)
|| property.Invoke(x).StartsWith(nextValue);
result = predicate.Expand();
}
return result;
}
我們可以這樣稱呼它:
var filterList = new List<string> { "1" , "2" }; // or more
var q = SessionInstance
.Query<Book>()
//.Where(x => filterList.Any(s => s.StartsWith(x.Code)))
.Where(filterList.AnyStarts<Contact>(x => x.Code))
;
我們將收到任何代碼以“ 1”,“ 2”,...開頭的書。
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