本文介绍了.NET Core Npgsql.EntityFrameworkCore ILikeExpression的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在使用EntityFramework Core和Npgsql提供程序，执行ILIKE查询工作正常：
I am using EntityFramework Core with Npgsql provider, perform ILIKE query works fine:
var query = dbContext.countries
.Where(w => (w.name != null &&
EF.Functions.ILike(w.name, $"{search}%")
);
到目前为止，查询已翻译成PostgreSQL的ILIKE。
Query is translated into PostgreSQL's ILIKE, so far so good.
我还在基于注释（模型中的[Searchable]或[Orderable]属性）构建动态LINQ，并且试图找出如何使用Expressions和Lambda执行ILIKE。代码：
I am also building a dynamic LINQ based on annotation - [Searchable] or [Orderable] properties in models - and I am trying to find out how to perform ILIKE using Expressions and Lambda. Code:
// works, except it produces just LIKE which is case sensitive. Not enough.
expr = Expression.Call(property, nameof(string.Contains), new Type[] { }, Expression.Constant(search));
// does not work, ends with exception, see below
expr = new Npgsql.EntityFrameworkCore.PostgreSQL.Query.Expressions.Internal.ILikeExpression(property, Expression.Constant(search_query));
有什么想法吗？谢谢！
// Exception
Application started. Press Ctrl+C to shut down.
fail: Microsoft.AspNetCore.Server.Kestrel[13]
Connection id "0HLGC19DMS3OI", Request id "0HLGC19DMS3OI:00000001": An unhandled exception was thrown by the application.
System.ArgumentException: must be reducible node
at System.Linq.Expressions.Expression.ReduceAndCheck()
at System.Linq.Expressions.Expression.ReduceExtensions()
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExtensionExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteLogicalBinaryExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteLogicalBinaryExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteLogicalBinaryExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteLogicalBinaryExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteLogicalBinaryExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression`1 lambda)
at System.Linq.Expressions.Expression`1.Accept(StackSpiller spiller)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteLambdaExpression(Expression expr)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression)
at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression)
at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression`1 lambda)
at System.Linq.Expressions.Expression`1.Accept(StackSpiller spiller)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteLambdaExpression(Expression expr)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression)
at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression)
at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression`1 lambda)
at System.Linq.Expressions.Expression`1.Accept(StackSpiller spiller)
at System.Linq.Expressions.Compiler.LambdaCompiler.Compile(LambdaExpression lambda)
at System.Linq.Expressions.Expression`1.Compile(Boolean preferInterpretation)
at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateExecutorLambda[TResults]()
at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateAsyncQueryExecutor[TResult](QueryModel queryModel)
at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken
cancellationToken)
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.CountAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
推荐答案
您需要发出与 EF.Functions.ILike（string，string）调用等效的表达式。
You need to emit the expression equivalent of the EF.Functions.ILike(string, string) call.
ILike 是静态扩展方法，定义为
ILike is a static extension method defined as
public static class NpgsqlDbFunctionsExtensions
{
public static bool ILike(this DbFunctions _, string matchExpression, string pattern);
}
和 Functions 是 EF 类的静态属性
public static class EF
{
public static DbFunctions Functions { get; }
}
因此，您要查找的表达式是这样的：
Hence the expression you are seeking is something like this:
expr = Expression.Call(
typeof(NpgsqlDbFunctionsExtensions),
nameof(NpgsqlDbFunctionsExtensions.ILike),
Type.EmptyTypes,
Expression.Property(null, typeof(EF), nameof(EF.Functions)),
property,
Expression.Constant(search)
);
这篇关于.NET Core Npgsql.EntityFrameworkCore ILikeExpression的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！