Question

我想创建一种储存模式,能够表达并利用Linq-To-Sql生成必要的文件。

例如,我有这样的职能:

// Possible criteria
Expression<Func<Purchase,bool>> criteria1 = p => p.Price > 1000;

// Function that should take that criteria and convert to SQL statement
static IEnumerable<Customer> GetCustomers (Expression<Func<Purchase,bool>> criteria)
{
   // ...
}

在这项职能方面,我谨将标准转化为使用Linq-To-Sql的LQ声明。

I am aware that you can use DataContext.Log to see the executed queries and DataContext.GetCommand(query).CommandText to see the full query before it is executed. However, I would like just a part of the entire expression generated.

我希望完成的工作是,使我的存放处能够把基础技术(Linq-to-Sql, Dapper, 等)抽象化。这样,我就能够向存放处转达,让它产生正确的声明,并利用正确的技术加以执行。

Answer 1

你可以这样做:

string sql = DataContext.GetTable<Customer>().Where(criteria).ToString();

ToString()让你表达。之后,你可以利用规章删除《惠予公约》条款。

Answer 2

这是我用来建立自己在职能地点使用的前提的法典。汇编者可以应付大量复杂的物体,因此,你必须这样做。

基本上,该法典通过了大量的(直观的法典、扼制的交换)标记,然后形成一种表达,以检索所有有安全保障的保安物体。法典 = 范围。守则和(安全) Id = 校正 Id = 图表。

CreateTrEntitiesAsync() simply returns a Entity Framework context, which has a DbSet Security property.

public async Task<Security[]> GetSecurities(IEnumerable<(string code, string exchange)> tickers)
{
    using (var ctx = await CreateTrEntitiesAsync())
    {
        var securityExpr = Expression.Parameter(typeof(Security), "security");
        Expression expr = null;
        Expression exprToadd;

        foreach (var item in tickers)
        {
            exprToadd = Expression.And(
                Expression.Equal(Expression.Property(securityExpr, nameof(Security.Code)), Expression.Constant(item.code)),
                Expression.Or(
                    Expression.Equal(Expression.Property(Expression.Property(securityExpr, nameof(Security.Exchange)), nameof(Exchange.MasterExchangeForStocksId)), Expression.Constant(item.exchange)),
                    Expression.Equal(Expression.Property(securityExpr, nameof(Security.ExchangeId)), Expression.Constant(item.exchange))
                )
            );

            if (expr == null)
                expr = exprToadd;
            else
                expr = Expression.Or(expr, exprToadd);
        }

        var criteria = Expression.Lambda<Func<Security, bool>>(expr, new ParameterExpression[] { securityExpr });
        var items = ctx.Securities.Where(criteria);
        return await items.ToArrayAsync();
    }
}

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