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

问题描述

我想从具有特定 accountID 的实体模型(我使用的是 EF 版本 5)获取记录列表.我得到了 tableName 字符串(必须是动态的)和 accountID.我正在尝试以下 2 种方法，但它们都不起作用(在 IQueryable 对象表"上给我错误:

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>();

<小时>

推荐答案

var query = table.Where(....).Select(...) 是正确的做法允许在运行时对查询构建器进行反射.但是，t.AccountID 是一个错误，因为 t 的类型仍然未知.

The var query = table.Where(....).Select(...) is the correct move as it allows reflection for the query builder at runtime. However, t.AccountID is an error because of the type of t remains unknown.

我以前在 LINQ to SQL 中使用过类似的方法，使用 System.Linq.Expressions.Expression，例如:

I've previously used a similar approach in LINQ to SQL, using System.Linq.Expressions.Expression, e.g.:

    // 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>();

如果您的对象有一个通用接口，则有一个更简单的语法:

If your object has a common interface there is a simpler syntax:

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;

如果您只需要支持几张表，您也可以这样做:

If you only have a few tables to support, you could do this as well:

    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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