如何从除某些列之外的表记录中选择 [英] How to Select from table records except some columns

问题描述

我有一个实体数据库，是从 sql 数据库创建的.我需要在 datagridview 上显示记录，我正在使用此代码.

I have a entity database, created from sql database. I need to show record on datagridview, i am using this code.

DBEntities db = new DBEntities();
dataGridView1.DataSource = db.Agent.Select(x => new { Name = x.Name, Second_Name = x.Second_Name}).ToList();

这是一个例子，真实的代理表包含大约 10 列，我需要显示所有，除了id".如果我每 8 列都做同样的事情，就会变成一个又长又无意义的行.怎么做才更健忘和好.

It's example, real agent table contain around 10 columns, and i need to show all, exept 'id'. If i do same for every 8 columns, become a long and senseless row. How to do it more obliviuous and good.

推荐答案

如果你不想使用匿名类型来指定你想要的字段，你可以:

If you don't want to use an anonymous type to specify the fields you want, you can:

1. 在结果集中使用 ID，或者
2. 包括 Select 中除 ID 之外的所有列，或
3. 使用映射库，例如 AutoMapper.

1. Live with having the ID in the result set, or
2. Include all of the columns in the Select except for the ID, or
3. Use a mapping library, like AutoMapper.

Linq 中没有 Select except 语句.但是，您可以使用此扩展方法来完成相同的事情:

There's no Select Except statement in Linq. However, you can use this extension method to accomplish the same thing:

/// <summary>
/// Returns all fields/properties from <paramref name="source"/> except for the field(s)/property(ies) listed in the selector expression.
/// </summary>
public static IQueryable SelectExcept<TSource, TResult>( this IQueryable<TSource> source, Expression<Func<TSource, TResult>> selector )
{
    var newExpression = selector.Body as NewExpression;

    var excludeProperties = newExpression != null
            ? newExpression.Members.Select( m => m.Name )
            : new[] { ( (MemberExpression)selector.Body ).Member.Name };

    var sourceType = typeof( TSource );
    var allowedSelectTypes = new Type[] { typeof( string ), typeof( ValueType ) };
    var sourceProperties = sourceType.GetProperties( BindingFlags.Public | BindingFlags.Instance ).Where( p => allowedSelectTypes.Any( t => t.IsAssignableFrom( ( (PropertyInfo)p ).PropertyType ) ) ).Select( p => ( (MemberInfo)p ).Name );
    var sourceFields = sourceType.GetFields( BindingFlags.Public | BindingFlags.Instance ).Where( f => allowedSelectTypes.Any( t => t.IsAssignableFrom( ( (FieldInfo)f ).FieldType ) ) ).Select( f => ( (MemberInfo)f ).Name );

    var selectFields = sourceProperties.Concat( sourceFields ).Where( p => !excludeProperties.Contains( p ) ).ToArray();

    var dynamicSelect = 
            string.Format( "new( {0} )",
                    string.Join( ", ", selectFields ) );

    return selectFields.Count() > 0
        ? source.Select( dynamicSelect )
        : Enumerable.Empty<TSource>().AsQueryable<TSource>();
}

进一步阅读
使用 SelectExcept 当你懒得打字

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