来自sql查询执行实体框架的匿名类型结果

Question

我正在使用实体框架5.0和.net framework 4.0代码的第一种方法。现在我知道我可以通过以下

在实体框架中运行原始sql

var students = Context.Database.SqlQuery<Student>("select * from student").ToList();

它工作得很好，但我想要的是返回匿名结果。例如，我只想要学生表中的特定列，如下面的

var students = Context.Database.SqlQuery<Student>("select FirstName from student").ToList();

它不起作用。它给出了异常

  

数据阅读器与指定的“MyApp.DataContext.Student”不兼容。类型为“StudentId”的成员在数据读取器中没有相应的具有相同名称的列。

所以我尝试了dynamic类型

var students = Context.Database.SqlQuery<dynamic>("select FirstName from student").ToList();

它也无效，它返回一个空对象。没有可用的数据。

有没有办法从动态SQL查询中获取匿名类型结果？

Answer 1

这是最终的解决方案，对我来说很好。

public static System.Collections.IEnumerable DynamicSqlQuery(this Database database, string sql, params object[] parameters)
        {
            TypeBuilder builder = createTypeBuilder(
                    "MyDynamicAssembly", "MyDynamicModule", "MyDynamicType");

            using (System.Data.IDbCommand command = database.Connection.CreateCommand())
            {
                try
                {
                    database.Connection.Open();
                    command.CommandText = sql;
                    command.CommandTimeout = command.Connection.ConnectionTimeout;
                    foreach (var param in parameters)
                    {
                        command.Parameters.Add(param);
                    }

                    using (System.Data.IDataReader reader = command.ExecuteReader())
                    {
                        var schema = reader.GetSchemaTable();

                        foreach (System.Data.DataRow row in schema.Rows)
                        {
                            string name = (string)row["ColumnName"];
                            //var a=row.ItemArray.Select(d=>d.)
                            Type type = (Type)row["DataType"];
                            if(type!=typeof(string) && (bool)row.ItemArray[schema.Columns.IndexOf("AllowDbNull")])
                            {
                                type = typeof(Nullable<>).MakeGenericType(type);
                            }
                            createAutoImplementedProperty(builder, name, type);
                        }
                    }
                }
                finally
                {
                    database.Connection.Close();
                    command.Parameters.Clear();
                }
            }

            Type resultType = builder.CreateType();

            return database.SqlQuery(resultType, sql, parameters);
        }

        private static TypeBuilder createTypeBuilder(
            string assemblyName, string moduleName, string typeName)
        {
            TypeBuilder typeBuilder = AppDomain
                .CurrentDomain
                .DefineDynamicAssembly(new AssemblyName(assemblyName),
                                       AssemblyBuilderAccess.Run)
                .DefineDynamicModule(moduleName)
                .DefineType(typeName, TypeAttributes.Public);
            typeBuilder.DefineDefaultConstructor(MethodAttributes.Public);
            return typeBuilder;
        }

        private static void createAutoImplementedProperty(
            TypeBuilder builder, string propertyName, Type propertyType)
        {
            const string PrivateFieldPrefix = "m_";
            const string GetterPrefix = "get_";
            const string SetterPrefix = "set_";

            // Generate the field.
            FieldBuilder fieldBuilder = builder.DefineField(
                string.Concat(PrivateFieldPrefix, propertyName),
                              propertyType, FieldAttributes.Private);

            // Generate the property
            PropertyBuilder propertyBuilder = builder.DefineProperty(
                propertyName, System.Reflection.PropertyAttributes.HasDefault, propertyType, null);

            // Property getter and setter attributes.
            MethodAttributes propertyMethodAttributes =
                MethodAttributes.Public | MethodAttributes.SpecialName |
                MethodAttributes.HideBySig;

            // Define the getter method.
            MethodBuilder getterMethod = builder.DefineMethod(
                string.Concat(GetterPrefix, propertyName),
                propertyMethodAttributes, propertyType, Type.EmptyTypes);

            // Emit the IL code.
            // ldarg.0
            // ldfld,_field
            // ret
            ILGenerator getterILCode = getterMethod.GetILGenerator();
            getterILCode.Emit(OpCodes.Ldarg_0);
            getterILCode.Emit(OpCodes.Ldfld, fieldBuilder);
            getterILCode.Emit(OpCodes.Ret);

            // Define the setter method.
            MethodBuilder setterMethod = builder.DefineMethod(
                string.Concat(SetterPrefix, propertyName),
                propertyMethodAttributes, null, new Type[] { propertyType });

            // Emit the IL code.
            // ldarg.0
            // ldarg.1
            // stfld,_field
            // ret
            ILGenerator setterILCode = setterMethod.GetILGenerator();
            setterILCode.Emit(OpCodes.Ldarg_0);
            setterILCode.Emit(OpCodes.Ldarg_1);
            setterILCode.Emit(OpCodes.Stfld, fieldBuilder);
            setterILCode.Emit(OpCodes.Ret);

            propertyBuilder.SetGetMethod(getterMethod);
            propertyBuilder.SetSetMethod(setterMethod);
        }    

Answer 2

您必须使用原始Sql，权限框架SqlQuery<T>仅适用于已知类型的对象。

这是我使用的方法：

public static IEnumerable<dynamic> DynamicListFromSql(this DbContext db, string Sql, Dictionary<string, object> Params)
{
    using (var cmd = db.Database.Connection.CreateCommand())
    {
        cmd.CommandText = Sql;
        if (cmd.Connection.State != ConnectionState.Open) { cmd.Connection.Open(); }

        foreach (KeyValuePair<string, object> p in Params)
        {
            DbParameter dbParameter = cmd.CreateParameter();
            dbParameter.ParameterName = p.Key;
            dbParameter.Value = p.Value;
            cmd.Parameters.Add(dbParameter);
        }

        using (var dataReader = cmd.ExecuteReader())
        {
            while (dataReader.Read())
            {
                var row = new ExpandoObject() as IDictionary<string, object>;
                for (var fieldCount = 0; fieldCount < dataReader.FieldCount; fieldCount++)
                {
                    row.Add(dataReader.GetName(fieldCount), dataReader[fieldCount]);
                }
                yield return row;
            }
        }
    }
}

您可以这样称呼它：

List<dynamic> results = DynamicListFromSql(myDb,"select * from table where a=@a and b=@b", new Dictionary<string, object> { { "a", true }, { "b", false } }).ToList();

Answer 3

您可以从这里尝试代码，向下滚动并找到stankovski的工具： http://www.codeproject.com/Articles/206416/Use-dynamic-type-in-Entity-Framework-SqlQuery

将代码复制到静态类后，您可以调用此函数来获得所需内容：

var students = Context.Database.DynamicSqlQuery("select FirstName from student").ToList()

Answer 4

如果你有一个实体并且你只想要一些属性，你可以在反射的帮助下获得更好的解决方案。

此代码建立在与上述答案相同的样本上。

除此之外，您还可以指定要返回的类型和字段数组。

结果是IEnumerable类型。

public static class DatabaseExtension
{
    public static IEnumerable<T> DynamicSqlQuery<T>(this Database database, string[] fields, string sql, params object[] parameters) where T : new()
    {
        var type = typeof (T);

        var builder = CreateTypeBuilder("MyDynamicAssembly", "MyDynamicModule", "MyDynamicType");

        foreach (var field in fields)
        {
            var prop = type.GetProperty(field);
            var propertyType = prop.PropertyType;
            CreateAutoImplementedProperty(builder, field, propertyType);
        }

        var resultType = builder.CreateType();

        var items = database.SqlQuery(resultType, sql, parameters);
        foreach (object item in items)
        {
            var obj = new T();
            var itemType = item.GetType();
            foreach (var prop in itemType.GetProperties(BindingFlags.Instance | BindingFlags.Public))
            {
                var name = prop.Name;
                var value = prop.GetValue(item, null);
                type.GetProperty(name).SetValue(obj, value);
            }
            yield return obj;
        }
    }

    private static TypeBuilder CreateTypeBuilder(string assemblyName, string moduleName, string typeName)
    {
        TypeBuilder typeBuilder = AppDomain
            .CurrentDomain
            .DefineDynamicAssembly(new AssemblyName(assemblyName), AssemblyBuilderAccess.Run)
            .DefineDynamicModule(moduleName)
            .DefineType(typeName, TypeAttributes.Public);
        typeBuilder.DefineDefaultConstructor(MethodAttributes.Public);
        return typeBuilder;
    }

    private static void CreateAutoImplementedProperty(TypeBuilder builder, string propertyName, Type propertyType)
    {
        const string privateFieldPrefix = "m_";
        const string getterPrefix = "get_";
        const string setterPrefix = "set_";

        // Generate the field.
        FieldBuilder fieldBuilder = builder.DefineField(
            string.Concat(privateFieldPrefix, propertyName),
                          propertyType, FieldAttributes.Private);

        // Generate the property
        PropertyBuilder propertyBuilder = builder.DefineProperty(
            propertyName, PropertyAttributes.HasDefault, propertyType, null);

        // Property getter and setter attributes.
        MethodAttributes propertyMethodAttributes =
            MethodAttributes.Public | MethodAttributes.SpecialName |
            MethodAttributes.HideBySig;

        // Define the getter method.
        MethodBuilder getterMethod = builder.DefineMethod(
            string.Concat(getterPrefix, propertyName),
            propertyMethodAttributes, propertyType, Type.EmptyTypes);

        // Emit the IL code.
        // ldarg.0
        // ldfld,_field
        // ret
        ILGenerator getterILCode = getterMethod.GetILGenerator();
        getterILCode.Emit(OpCodes.Ldarg_0);
        getterILCode.Emit(OpCodes.Ldfld, fieldBuilder);
        getterILCode.Emit(OpCodes.Ret);

        // Define the setter method.
        MethodBuilder setterMethod = builder.DefineMethod(
            string.Concat(setterPrefix, propertyName),
            propertyMethodAttributes, null, new Type[] { propertyType });

        // Emit the IL code.
        // ldarg.0
        // ldarg.1
        // stfld,_field
        // ret
        ILGenerator setterILCode = setterMethod.GetILGenerator();
        setterILCode.Emit(OpCodes.Ldarg_0);
        setterILCode.Emit(OpCodes.Ldarg_1);
        setterILCode.Emit(OpCodes.Stfld, fieldBuilder);
        setterILCode.Emit(OpCodes.Ret);

        propertyBuilder.SetGetMethod(getterMethod);
        propertyBuilder.SetSetMethod(setterMethod);
    }    
}

您可以这样称呼它：

var fields = new[]{ "Id", "FirstName", "LastName" };
var sql = string.Format("SELECT {0} FROM People WHERE Id = @id", string.Join(", ", fields));

var person = db.Database.DynamicSqlQuery<People>(fields, sql, new SqlParameter("id", id))
    .FirstOrDefault();

实际上它仅适用于简单类型，并且没有错误处理。

Answer 5

我那样使用它

ORMClass：

related_name

方法：

'+'

最后使用

public class ORMBase<T, TContext> : IORM<T>
        where T : class
        where TContext : DbContext, IDisposable, new()

Answer 6

我知道这可能会稍晚一些，但是如果您想执行Scalar函数并将其始终转换为统一类型，则可以使用这种方法。

只需使用此 forceStringCast 参数将sql标量函数结果强制转换为字符串，然后根据需要使用此字符串。

public static Task<T> ScalarFunction<T>(DbContext db, string sql, bool forceStringCast = false, Dictionary<string, object> parameters = null) 
    {
        string cmdText;

        if (forceStringCast)
        {
            cmdText = $@"SELECT CAST({sql}({string.Join(",", 
                parameters.Keys.Select(p => "@" + p).ToList())} AS VARCHAR(MAX)));";
        }
        else
        {
            cmdText =
                $@"SELECT {sql}({string.Join(",", 
                    parameters.Keys.Select(p => "@" + p).ToList())});";
        }

        return db.Database.SqlQuery<T>(cmdText,parameters.Select(p => new SqlParameter(p.Key, p.Value)).ToArray()).FirstOrDefaultAsync();
    }

Answer 7

这是我的解决方案：

DbContext.Database.Connection.Open();

            var cmd = DbContext.Database.Connection.CreateCommand();
            cmd.CommandText = @"Select * from Table where Param1 = @Param1 and Param2 = @Param2";
            cmd.Parameters.Add(new SqlParameter("Param1", Mahdi));
            cmd.Parameters.Add(new SqlParameter("Param2", 20));

            List<Dictionary<string, object>> items = new List<Dictionary<string, object>>();
            var reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                Dictionary<string, object> item = new Dictionary<string, object>();

                for (int i = 0; i < reader.FieldCount; i++)
                    item[reader.GetName(i)] = (reader[i]);
                items.Add(item);
            }

            return Request.CreateResponse(HttpStatusCode.OK, items);

希望对大家有帮助;)