LINQ从动态tableName字符串中选择 [英] LINQ Select from dynamic tableName string

问题描述

我想从一个实体模型（我使用EF版本5）获取一个特定accountID的记录列表。我被提供了tableName字符串（这必须是动态的）和accountID。我正在尝试以下2种方法，但没有一个是工作的（给我的错误在IQueryable对象'表'：

I want to get list of records from an entity model (I'm using EF version 5) with a particular accountID. I'm being supplied with the tableName string (this has to be dynamic) and the accountID. I'm trying the following 2 methods but none of them is working (giving me errors on the IQueryable object 'table':

PropertyInfo info = _db.GetType().GetProperty(tableName);
IQueryable table = info.GetValue(_db, null) as IQueryable;

var query = table.Where(t => t.AccountID == accID)
                        .Select(t => t);

List <object> recList = (   from records in table
                            where records.AccountID == accID
                            select records).ToList<object>();

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推荐答案

var query = table.Where（....） （...）是正确的移动，并允许在运行时反映像查询构建器。

The var query = table.Where(....).Select(...) is correct move, and that allows reflection like query builder in runtime.

但是， t .AccountID 是一个错误，因为 t 的类型仍然未知。

However, t.AccountID is an error because of the type of t remain unknown.

我已经做了很多年前类似的你唱 System.Linq.Expressions .Expression 直接在Linq2Sql中。

I have done many years ago similar by using System.Linq.Expressions.Expression directly in Linq2Sql.

eg

// NOT TESTED
var table=context.GetTable(dynamicTableName);
var theT=table.Experssion; // actually, I forget. DynamicExpression  or MemberBinding? or
var theField=Expression.Field(theT, "AccountID"); // or dynamic name
var query=table.Where(Expression.Equal(theField, accID);
var recList=query.ToList<object>();

我记得应该是一个更简单的语法，如果你的对象有共同的界面

I remember that should a easier syntax, if you object has common interface

IQueryable<MyInterface> table = context.GetTable("table") as IQueryable<MyInterface>;
var recList=from r in table
            where table.AccountID == ac // if your AccountID is on MyInterface
            select table;

或者，如果您只有几个表格来支持。

Or, if you only have a few table to support.

IQueryable<MyInterface> table;
if("table1"==tableName)
   table=_db.table1
elseif("table2"==tableName)
   table=_db.table2
elseif("table3"==tableName)
   table=_db.table3
else
   throw exception

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