linq - 如何使用 System.Linq.Dynamic 命名空间在 Dynamic Linq 中执行以下操作

Question

我只想知道如何使用 System.Linq.Dynamic 命名空间在 Dynamic Linq 中执行以下操作

var query2 = db.Customers.Select(
                    cust => new Customer
                    {
                        FirstName = cust.FirstName,
                        LastName = cust.LastName
                        Tags="sampleTag,Tag"
                    }
                ).ToList<Customer>();

我能够使其动态化，但我不能在此处包含标签:

var query1 = db.Customers.Select<Customer>("new (FirstName, LastName)");

或者如果有其他建议，非常欢迎。 :)

**Below is the code --> the System.Linq.Dynamic namespace:**

//Copyright (C) Microsoft Corporation.  All rights reserved.
//http://stackoverflow.com/questions/1465700/system-linq-dynamic-select-new-into-a-listt-or-any-other-enumerable


using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Reflection.Emit;
using System.Threading;

namespace System.Linq.Dynamic
{
    public static class DynamicQueryable
    {
        public static IQueryable<T> Where<T>(this IQueryable<T> source, string predicate, params object[] values)
        {
            return (IQueryable<T>)Where((IQueryable)source, predicate, values);
        }

        public static IQueryable Where(this IQueryable source, string predicate, params object[] values)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (predicate == null) throw new ArgumentNullException("predicate");
            LambdaExpression lambda = DynamicExpression.ParseLambda(source.ElementType, typeof(bool), predicate, values);
            return source.Provider.CreateQuery(
                Expression.Call(
                    typeof(Queryable), "Where",
                    new Type[] { source.ElementType },
                    source.Expression, Expression.Quote(lambda)));
        }

        public static IQueryable<TResult> Select<TResult>(this IQueryable source, string selector, params object[] values)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (selector == null) throw new ArgumentNullException("selector");
            LambdaExpression lambda = DynamicExpression.ParseLambda(source.ElementType, typeof(TResult), selector, values);
            return source.Provider.CreateQuery<TResult>(
                Expression.Call(
                    typeof(Queryable), "Select",
                    new Type[] { source.ElementType, typeof(TResult) },
                    source.Expression, Expression.Quote(lambda)));
        }

        public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string ordering, params object[] values)
        {
            return (IQueryable<T>)OrderBy((IQueryable)source, ordering, values);
        }

        public static IQueryable OrderBy(this IQueryable source, string ordering, params object[] values)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (ordering == null) throw new ArgumentNullException("ordering");
            ParameterExpression[] parameters = new ParameterExpression[] {
                Expression.Parameter(source.ElementType, "") };
            ExpressionParser parser = new ExpressionParser(parameters, ordering, values);
            IEnumerable<DynamicOrdering> orderings = parser.ParseOrdering();
            Expression queryExpr = source.Expression;
            string methodAsc = "OrderBy";
            string methodDesc = "OrderByDescending";
            foreach (DynamicOrdering o in orderings)
            {
                queryExpr = Expression.Call(
                    typeof(Queryable), o.Ascending ? methodAsc : methodDesc,
                    new Type[] { source.ElementType, o.Selector.Type },
                    queryExpr, Expression.Quote(Expression.Lambda(o.Selector, parameters)));
                methodAsc = "ThenBy";
                methodDesc = "ThenByDescending";
            }
            return source.Provider.CreateQuery(queryExpr);
        }

        public static IQueryable Take(this IQueryable source, int count)
        {
            if (source == null) throw new ArgumentNullException("source");
            return source.Provider.CreateQuery(
                Expression.Call(
                    typeof(Queryable), "Take",
                    new Type[] { source.ElementType },
                    source.Expression, Expression.Constant(count)));
        }

        public static IQueryable Skip(this IQueryable source, int count)
        {
            if (source == null) throw new ArgumentNullException("source");
            return source.Provider.CreateQuery(
                Expression.Call(
                    typeof(Queryable), "Skip",
                    new Type[] { source.ElementType },
                    source.Expression, Expression.Constant(count)));
        }

        public static IQueryable GroupBy(this IQueryable source, string keySelector, string elementSelector, params object[] values)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (keySelector == null) throw new ArgumentNullException("keySelector");
            if (elementSelector == null) throw new ArgumentNullException("elementSelector");
            LambdaExpression keyLambda = DynamicExpression.ParseLambda(source.ElementType, null, keySelector, values);
            LambdaExpression elementLambda = DynamicExpression.ParseLambda(source.ElementType, null, elementSelector, values);
            return source.Provider.CreateQuery(
                Expression.Call(
                    typeof(Queryable), "GroupBy",
                    new Type[] { source.ElementType, keyLambda.Body.Type, elementLambda.Body.Type },
                    source.Expression, Expression.Quote(keyLambda), Expression.Quote(elementLambda)));
        }

        public static bool Any(this IQueryable source)
        {
            if (source == null) throw new ArgumentNullException("source");
            return (bool)source.Provider.Execute(
                Expression.Call(
                    typeof(Queryable), "Any",
                    new Type[] { source.ElementType }, source.Expression));
        }

        public static int Count(this IQueryable source)
        {
            if (source == null) throw new ArgumentNullException("source");
            return (int)source.Provider.Execute(
                Expression.Call(
                    typeof(Queryable), "Count",
                    new Type[] { source.ElementType }, source.Expression));
        }
    }

    public abstract class DynamicClass
    {
        public override string ToString()
        {
            PropertyInfo[] props = this.GetType().GetProperties(BindingFlags.Instance | BindingFlags.Public);
            StringBuilder sb = new StringBuilder();
            sb.Append("{");
            for (int i = 0; i < props.Length; i++)
            {
                if (i > 0) sb.Append(", ");
                sb.Append(props[i].Name);
                sb.Append("=");
                sb.Append(props[i].GetValue(this, null));
            }
            sb.Append("}");
            return sb.ToString();
        }
    }

    public class DynamicProperty
    {
        string name;
        Type type;

        public DynamicProperty(string name, Type type)
        {
            if (name == null) throw new ArgumentNullException("name");
            if (type == null) throw new ArgumentNullException("type");
            this.name = name;
            this.type = type;
        }

        public string Name
        {
            get { return name; }
        }

        public Type Type
        {
            get { return type; }
        }
    }

    public static class DynamicExpression
    {
        public static Expression Parse(Type resultType, string expression, params object[] values)
        {
            ExpressionParser parser = new ExpressionParser(null, expression, values);
            return parser.Parse(resultType);
        }

        public static LambdaExpression ParseLambda(Type itType, Type resultType, string expression, params object[] values)
        {
            return ParseLambda(new ParameterExpression[] { Expression.Parameter(itType, "") }, resultType, expression, values);
        }

        public static LambdaExpression ParseLambda(ParameterExpression[] parameters, Type resultType, string expression, params object[] values)
        {
            ExpressionParser parser = new ExpressionParser(parameters, expression, values);
            return Expression.Lambda(parser.Parse(resultType), parameters);
        }

        public static Expression<Func<T, S>> ParseLambda<T, S>(string expression, params object[] values)
        {
            return (Expression<Func<T, S>>)ParseLambda(typeof(T), typeof(S), expression, values);
        }

        public static Type CreateClass(params DynamicProperty[] properties)
        {
            return ClassFactory.Instance.GetDynamicClass(properties);
        }

        public static Type CreateClass(IEnumerable<DynamicProperty> properties)
        {
            return ClassFactory.Instance.GetDynamicClass(properties);
        }
    }

    internal class DynamicOrdering
    {
        public Expression Selector;
        public bool Ascending;
    }

    internal class Signature : IEquatable<Signature>
    {
        public DynamicProperty[] properties;
        public int hashCode;

        public Signature(IEnumerable<DynamicProperty> properties)
        {
            this.properties = properties.ToArray();
            hashCode = 0;
            foreach (DynamicProperty p in properties)
            {
                hashCode ^= p.Name.GetHashCode() ^ p.Type.GetHashCode();
            }
        }

        public override int GetHashCode()
        {
            return hashCode;
        }

        public override bool Equals(object obj)
        {
            return obj is Signature ? Equals((Signature)obj) : false;
        }

        public bool Equals(Signature other)
        {
            if (properties.Length != other.properties.Length) return false;
            for (int i = 0; i < properties.Length; i++)
            {
                if (properties[i].Name != other.properties[i].Name ||
                    properties[i].Type != other.properties[i].Type) return false;
            }
            return true;
        }
    }

    internal class ClassFactory
    {
        public static readonly ClassFactory Instance = new ClassFactory();

        static ClassFactory() { }  // Trigger lazy initialization of static fields

        ModuleBuilder module;
        Dictionary<Signature, Type> classes;
        int classCount;
        ReaderWriterLock rwLock;

        private ClassFactory()
        {
            AssemblyName name = new AssemblyName("DynamicClasses");
            AssemblyBuilder assembly = AppDomain.CurrentDomain.DefineDynamicAssembly(name, AssemblyBuilderAccess.Run);
#if ENABLE_LINQ_PARTIAL_TRUST
            new ReflectionPermission(PermissionState.Unrestricted).Assert();
#endif
            try
            {
                module = assembly.DefineDynamicModule("Module");
            }
            finally
            {
#if ENABLE_LINQ_PARTIAL_TRUST
                PermissionSet.RevertAssert();
#endif
            }
            classes = new Dictionary<Signature, Type>();
            rwLock = new ReaderWriterLock();
        }

        public Type GetDynamicClass(IEnumerable<DynamicProperty> properties)
        {
            rwLock.AcquireReaderLock(Timeout.Infinite);
            try
            {
                Signature signature = new Signature(properties);
                Type type;
                if (!classes.TryGetValue(signature, out type))
                {
                    type = CreateDynamicClass(signature.properties);
                    classes.Add(signature, type);
                }
                return type;
            }
            finally
            {
                rwLock.ReleaseReaderLock();
            }
        }

        Type CreateDynamicClass(DynamicProperty[] properties)
        {
            LockCookie cookie = rwLock.UpgradeToWriterLock(Timeout.Infinite);
            try
            {
                string typeName = "DynamicClass" + (classCount + 1);
#if ENABLE_LINQ_PARTIAL_TRUST
                new ReflectionPermission(PermissionState.Unrestricted).Assert();
#endif
                try
                {
                    TypeBuilder tb = this.module.DefineType(typeName, TypeAttributes.Class |
                        TypeAttributes.Public, typeof(DynamicClass));
                    FieldInfo[] fields = GenerateProperties(tb, properties);
                    GenerateEquals(tb, fields);
                    GenerateGetHashCode(tb, fields);
                    Type result = tb.CreateType();
                    classCount++;
                    return result;
                }
                finally
                {
#if ENABLE_LINQ_PARTIAL_TRUST
                    PermissionSet.RevertAssert();
#endif
                }
            }
            finally
            {
                rwLock.DowngradeFromWriterLock(ref cookie);
            }
        }

        FieldInfo[] GenerateProperties(TypeBuilder tb, DynamicProperty[] properties)
        {
            FieldInfo[] fields = new FieldBuilder[properties.Length];
            for (int i = 0; i < properties.Length; i++)
            {
                DynamicProperty dp = properties[i];
                FieldBuilder fb = tb.DefineField("_" + dp.Name, dp.Type, FieldAttributes.Private);
                PropertyBuilder pb = tb.DefineProperty(dp.Name, PropertyAttributes.HasDefault, dp.Type, null);
                MethodBuilder mbGet = tb.DefineMethod("get_" + dp.Name,
                    MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig,
                    dp.Type, Type.EmptyTypes);
                ILGenerator genGet = mbGet.GetILGenerator();
                genGet.Emit(OpCodes.Ldarg_0);
                genGet.Emit(OpCodes.Ldfld, fb);
                genGet.Emit(OpCodes.Ret);
                MethodBuilder mbSet = tb.DefineMethod("set_" + dp.Name,
                    MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig,
                    null, new Type[] { dp.Type });
                ILGenerator genSet = mbSet.GetILGenerator();
                genSet.Emit(OpCodes.Ldarg_0);
                genSet.Emit(OpCodes.Ldarg_1);
                genSet.Emit(OpCodes.Stfld, fb);
                genSet.Emit(OpCodes.Ret);
                pb.SetGetMethod(mbGet);
                pb.SetSetMethod(mbSet);
                fields[i] = fb;
            }
            return fields;
        }

        void GenerateEquals(TypeBuilder tb, FieldInfo[] fields)
        {
            MethodBuilder mb = tb.DefineMethod("Equals",
                MethodAttributes.Public | MethodAttributes.ReuseSlot |
                MethodAttributes.Virtual | MethodAttributes.HideBySig,
                typeof(bool), new Type[] { typeof(object) });
            ILGenerator gen = mb.GetILGenerator();
            LocalBuilder other = gen.DeclareLocal(tb);
            Label next = gen.DefineLabel();
            gen.Emit(OpCodes.Ldarg_1);
            gen.Emit(OpCodes.Isinst, tb);
            gen.Emit(OpCodes.Stloc, other);
            gen.Emit(OpCodes.Ldloc, other);
            gen.Emit(OpCodes.Brtrue_S, next);
            gen.Emit(OpCodes.Ldc_I4_0);
            gen.Emit(OpCodes.Ret);
            gen.MarkLabel(next);
            foreach (FieldInfo field in fields)
            {
                Type ft = field.FieldType;
                Type ct = typeof(EqualityComparer<>).MakeGenericType(ft);
                next = gen.DefineLabel();
                gen.EmitCall(OpCodes.Call, ct.GetMethod("get_Default"), null);
                gen.Emit(OpCodes.Ldarg_0);
                gen.Emit(OpCodes.Ldfld, field);
                gen.Emit(OpCodes.Ldloc, other);
                gen.Emit(OpCodes.Ldfld, field);
                gen.EmitCall(OpCodes.Callvirt, ct.GetMethod("Equals", new Type[] { ft, ft }), null);
                gen.Emit(OpCodes.Brtrue_S, next);
                gen.Emit(OpCodes.Ldc_I4_0);
                gen.Emit(OpCodes.Ret);
                gen.MarkLabel(next);
            }
            gen.Emit(OpCodes.Ldc_I4_1);
            gen.Emit(OpCodes.Ret);
        }

        void GenerateGetHashCode(TypeBuilder tb, FieldInfo[] fields)
        {
            MethodBuilder mb = tb.DefineMethod("GetHashCode",
                MethodAttributes.Public | MethodAttributes.ReuseSlot |
                MethodAttributes.Virtual | MethodAttributes.HideBySig,
                typeof(int), Type.EmptyTypes);
            ILGenerator gen = mb.GetILGenerator();
            gen.Emit(OpCodes.Ldc_I4_0);
            foreach (FieldInfo field in fields)
            {
                Type ft = field.FieldType;
                Type ct = typeof(EqualityComparer<>).MakeGenericType(ft);
                gen.EmitCall(OpCodes.Call, ct.GetMethod("get_Default"), null);
                gen.Emit(OpCodes.Ldarg_0);
                gen.Emit(OpCodes.Ldfld, field);
                gen.EmitCall(OpCodes.Callvirt, ct.GetMethod("GetHashCode", new Type[] { ft }), null);
                gen.Emit(OpCodes.Xor);
            }
            gen.Emit(OpCodes.Ret);
        }
    }

    public sealed class ParseException : Exception
    {
        int position;

        public ParseException(string message, int position)
            : base(message)
        {
            this.position = position;
        }

        public int Position
        {
            get { return position; }
        }

        public override string ToString()
        {
            return string.Format(Res.ParseExceptionFormat, Message, position);
        }
    }

    internal class ExpressionParser
    {
        struct Token
        {
            public TokenId id;
            public string text;
            public int pos;
        }

        enum TokenId
        {
            Unknown,
            End,
            Identifier,
            StringLiteral,
            IntegerLiteral,
            RealLiteral,
            Exclamation,
            Percent,
            Amphersand,
            OpenParen,
            CloseParen,
            Asterisk,
            Plus,
            Comma,
            Minus,
            Dot,
            Slash,
            Colon,
            LessThan,
            Equal,
            GreaterThan,
            Question,
            OpenBracket,
            CloseBracket,
            Bar,
            ExclamationEqual,
            DoubleAmphersand,
            LessThanEqual,
            LessGreater,
            DoubleEqual,
            GreaterThanEqual,
            DoubleBar
        }

        interface ILogicalSignatures
        {
            void F(bool x, bool y);
            void F(bool? x, bool? y);
        }

        interface IArithmeticSignatures
        {
            void F(int x, int y);
            void F(uint x, uint y);
            void F(long x, long y);
            void F(ulong x, ulong y);
            void F(float x, float y);
            void F(double x, double y);
            void F(decimal x, decimal y);
            void F(int? x, int? y);
            void F(uint? x, uint? y);
            void F(long? x, long? y);
            void F(ulong? x, ulong? y);
            void F(float? x, float? y);
            void F(double? x, double? y);
            void F(decimal? x, decimal? y);
        }

        interface IRelationalSignatures : IArithmeticSignatures
        {
            void F(string x, string y);
            void F(char x, char y);
            void F(DateTime x, DateTime y);
            void F(TimeSpan x, TimeSpan y);
            void F(char? x, char? y);
            void F(DateTime? x, DateTime? y);
            void F(TimeSpan? x, TimeSpan? y);
        }

        interface IEqualitySignatures : IRelationalSignatures
        {
            void F(bool x, bool y);
            void F(bool? x, bool? y);
        }

        interface IAddSignatures : IArithmeticSignatures
        {
            void F(DateTime x, TimeSpan y);
            void F(TimeSpan x, TimeSpan y);
            void F(DateTime? x, TimeSpan? y);
            void F(TimeSpan? x, TimeSpan? y);
        }

        interface ISubtractSignatures : IAddSignatures
        {
            void F(DateTime x, DateTime y);
            void F(DateTime? x, DateTime? y);
        }

        interface INegationSignatures
        {
            void F(int x);
            void F(long x);
            void F(float x);
            void F(double x);
            void F(decimal x);
            void F(int? x);
            void F(long? x);
            void F(float? x);
            void F(double? x);
            void F(decimal? x);
        }

        interface INotSignatures
        {
            void F(bool x);
            void F(bool? x);
        }

        interface IEnumerableSignatures
        {
            void Where(bool predicate);
            void Any();
            void Any(bool predicate);
            void All(bool predicate);
            void Count();
            void Count(bool predicate);
            void Min(object selector);
            void Max(object selector);
            void Sum(int selector);
            void Sum(int? selector);
            void Sum(long selector);
            void Sum(long? selector);
            void Sum(float selector);
            void Sum(float? selector);
            void Sum(double selector);
            void Sum(double? selector);
            void Sum(decimal selector);
            void Sum(decimal? selector);
            void Average(int selector);
            void Average(int? selector);
            void Average(long selector);
            void Average(long? selector);
            void Average(float selector);
            void Average(float? selector);
            void Average(double selector);
            void Average(double? selector);
            void Average(decimal selector);
            void Average(decimal? selector);
        }

        static readonly Type[] predefinedTypes = {
            typeof(Object),
            typeof(Boolean),
            typeof(Char),
            typeof(String),
            typeof(SByte),
            typeof(Byte),
            typeof(Int16),
            typeof(UInt16),
            typeof(Int32),
            typeof(UInt32),
            typeof(Int64),
            typeof(UInt64),
            typeof(Single),
            typeof(Double),
            typeof(Decimal),
            typeof(DateTime),
            typeof(TimeSpan),
            typeof(Guid),
            typeof(Math),
            typeof(Convert)
        };

        static readonly Expression trueLiteral = Expression.Constant(true);
        static readonly Expression falseLiteral = Expression.Constant(false);
        static readonly Expression nullLiteral = Expression.Constant(null);

        static readonly string keywordIt = "it";
        static readonly string keywordIif = "iif";
        static readonly string keywordNew = "new";

        static Dictionary<string, object> keywords;

        Dictionary<string, object> symbols;
        IDictionary<string, object> externals;
        Dictionary<Expression, string> literals;
        ParameterExpression it;
        string text;
        int textPos;
        int textLen;
        char ch;
        Token token;

        public ExpressionParser(ParameterExpression[] parameters, string expression, object[] values)
        {
            if (expression == null) throw new ArgumentNullException("expression");
            if (keywords == null) keywords = CreateKeywords();
            symbols = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
            literals = new Dictionary<Expression, string>();
            if (parameters != null) ProcessParameters(parameters);
            if (values != null) ProcessValues(values);
            text = expression;
            textLen = text.Length;
            SetTextPos(0);
            NextToken();
        }

        void ProcessParameters(ParameterExpression[] parameters)
        {
            foreach (ParameterExpression pe in parameters)
                if (!String.IsNullOrEmpty(pe.Name))
                    AddSymbol(pe.Name, pe);
            if (parameters.Length == 1 && String.IsNullOrEmpty(parameters[0].Name))
                it = parameters[0];
        }

        void ProcessValues(object[] values)
        {
            for (int i = 0; i < values.Length; i++)
            {
                object value = values[i];
                if (i == values.Length - 1 && value is IDictionary<string, object>)
                {
                    externals = (IDictionary<string, object>)value;
                }
                else
                {
                    AddSymbol("@" + i.ToString(System.Globalization.CultureInfo.InvariantCulture), value);
                }
            }
        }

        void AddSymbol(string name, object value)
        {
            if (symbols.ContainsKey(name))
                throw ParseError(Res.DuplicateIdentifier, name);
            symbols.Add(name, value);
        }

        private Type newResultType;
        public Expression Parse(Type resultType)
        {
            newResultType = resultType;
            int exprPos = token.pos;
            Expression expr = ParseExpression();
            if (resultType != null)
                if ((expr = PromoteExpression(expr, resultType, true)) == null)
                    throw ParseError(exprPos, Res.ExpressionTypeMismatch, GetTypeName(resultType));
            ValidateToken(TokenId.End, Res.SyntaxError);
            return expr;
        }

#pragma warning disable 0219
        public IEnumerable<DynamicOrdering> ParseOrdering()
        {
            List<DynamicOrdering> orderings = new List<DynamicOrdering>();
            while (true)
            {
                Expression expr = ParseExpression();
                bool ascending = true;
                if (TokenIdentifierIs("asc") || TokenIdentifierIs("ascending"))

Answer 1

我试过这个:

using System;
using System.Linq;
using System.Linq.Dynamic;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    public class Customer
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Tags { get; set; }
    }


    class Program
    {
        static void Main( string[] args )
        {

            var Customers = new List<Customer>(){ new Customer(){ FirstName = "test", LastName = "case"}};

            var query2 = Customers.Select(
                    cust => new Customer
                    {
                        FirstName = cust.FirstName,
                        LastName = cust.LastName,
                        Tags="sampleTag,Tag"
                    }
                ).ToList<Customer>();


            var query1 = Customers.AsQueryable().Select( "new (FirstName, LastName, \"sampleTag,Tag\" AS Tags)" );

            foreach(dynamic cust in query1)
            {
                Console.WriteLine(cust.Tags);
            }

            Console.ReadLine();
        }
    }
}