linq to sql startwith性能索引列

Question

我首先使用实体​​代码。 索引列：

• SourceCatalogId
• 残疾人
• CategoryPath

40 000表中的行，

我的问题是，查询需要40秒！通过SQL事件探查器

var result = DBContext.Set<SourceProduct>() 
      .Include(x => x.SalesHistories, x => x.SourceCatalog) 
      .Where(p => p.SourceCatalogId == 2) 
      .where(p => p.Disabled == false) 
      .where(x => x.CategoryPath.StartsWith("MyPath")) 
      .orderby(x => x.ShortDesignation) 
      .Skip(1) 
      .Take(10) 
      .toList(); 

SQL：

exec sp_executesql N'SELECT TOP (10) 
[Project1].[SourceProductId] AS [SourceProductId], 
[Project1].[SourceSKU] AS [SourceSKU], 
[Project1].[SourceCatalogId] AS [SourceCatalogId], 
[Project1].[ManufacturerReference] AS [ManufacturerReference], 
[Project1].[Disabled] AS [Disabled], 
[Project1].[EAN] AS [EAN], 
[Project1].[ShortDesignation] AS [ShortDesignation], 
[Project1].[FullDesignation] AS [FullDesignation], 
[Project1].[Description] AS [Description], 
[Project1].[Url] AS [Url], 
[Project1].[CategoryPath] AS [CategoryPath], 
[Project1].[Condition] AS [Condition], 
[Project1].[BuyingPriceHT] AS [BuyingPriceHT], 
[Project1].[ShippingPriceHT] AS [ShippingPriceHT], 
[Project1].[PublicSellingPriceHT] AS [PublicSellingPriceHT], 
[Project1].[PictureUrl1] AS [PictureUrl1], 
[Project1].[PictureUrl2] AS [PictureUrl2], 
[Project1].[PictureUrl3] AS [PictureUrl3], 
[Project1].[PictureUrl4] AS [PictureUrl4], 
[Project1].[Quantity] AS [Quantity], 
[Project1].[AddDate] AS [AddDate], 
[Project1].[UpdateDate] AS [UpdateDate], 
[Project1].[Followers] AS [Followers] 
FROM (SELECT [Project1].[SourceProductId] AS [SourceProductId], [Project1].[SourceSKU] AS [SourceSKU], [Project1].[SourceCatalogId] AS [SourceCatalogId], [Project1].[ManufacturerReference] AS [ManufacturerReference], [Project1].[Disabled] AS [Disabled], [Project1].[EAN] AS [EAN], [Project1].[ShortDesignation] AS [ShortDesignation], [Project1].[FullDesignation] AS [FullDesignation], [Project1].[Description] AS [Description], [Project1].[Url] AS [Url], [Project1].[CategoryPath] AS [CategoryPath], [Project1].[Condition] AS [Condition], [Project1].[BuyingPriceHT] AS [BuyingPriceHT], [Project1].[ShippingPriceHT] AS [ShippingPriceHT], [Project1].[PublicSellingPriceHT] AS [PublicSellingPriceHT], [Project1].[PictureUrl1] AS [PictureUrl1], [Project1].[PictureUrl2] AS [PictureUrl2], [Project1].[PictureUrl3] AS [PictureUrl3], [Project1].[PictureUrl4] AS [PictureUrl4], [Project1].[Quantity] AS [Quantity], [Project1].[AddDate] AS [AddDate], [Project1].[UpdateDate] AS [UpdateDate], [Project1].[Followers] AS [Followers], row_number() OVER (ORDER BY [Project1].[ShortDesignation] ASC) AS [row_number] 
    FROM (SELECT 
     [Extent1].[SourceProductId] AS [SourceProductId], 
     [Extent1].[SourceSKU] AS [SourceSKU], 
     [Extent1].[SourceCatalogId] AS [SourceCatalogId], 
     [Extent1].[ManufacturerReference] AS [ManufacturerReference], 
     [Extent1].[Disabled] AS [Disabled], 
     [Extent1].[EAN] AS [EAN], 
     [Extent1].[ShortDesignation] AS [ShortDesignation], 
     [Extent1].[FullDesignation] AS [FullDesignation], 
     [Extent1].[Description] AS [Description], 
     [Extent1].[Url] AS [Url], 
     [Extent1].[CategoryPath] AS [CategoryPath], 
     [Extent1].[Condition] AS [Condition], 
     [Extent1].[BuyingPriceHT] AS [BuyingPriceHT], 
     [Extent1].[ShippingPriceHT] AS [ShippingPriceHT], 
     [Extent1].[PublicSellingPriceHT] AS [PublicSellingPriceHT], 
     [Extent1].[PictureUrl1] AS [PictureUrl1], 
     [Extent1].[PictureUrl2] AS [PictureUrl2], 
     [Extent1].[PictureUrl3] AS [PictureUrl3], 
     [Extent1].[PictureUrl4] AS [PictureUrl4], 
     [Extent1].[Quantity] AS [Quantity], 
     [Extent1].[AddDate] AS [AddDate], 
     [Extent1].[UpdateDate] AS [UpdateDate], 
     [Extent1].[Followers] AS [Followers] 
     FROM [dbo].[SourceProducts] AS [Extent1] 
     WHERE ([Extent1].[SourceCatalogId] = @p__linq__0) AND (0 = [Extent1].[Disabled]) AND ([Extent1].[CategoryPath] LIKE @p__linq__1 ESCAPE N''~'') 
    ) AS [Project1] 
) AS [Project1] 
WHERE [Project1].[row_number] > 0 
ORDER BY [Project1].[ShortDesignation] ASC',N'@p__linq__0 bigint,@p__linq__1 nvarchar(4000)',@p__linq__0=2,@p__linq__1=N'MyPath%' 

在之前的最后一个where子句，如果我删除 “逃生N '' 〜 ''”：

WHERE ([Extent1].[SourceCatalogId] = @p__linq__0) AND (0 = [Extent1].[Disabled]) AND ([Extent1].[CategoryPath] LIKE @p__linq__1 ESCAPE N''~'') 

查询需要4s。

这是正常的吗？索引用途？我可以用startWith解决它吗？

编辑

为categoryPath指数attribut：

[Index("IX_SourceProduct_SourceCatalogId_Disabled_CategoryPath", 3), StringLength(400)] 
    public string CategoryPath { get; set; } 

EDIT2

确定我的事，我是非常接近，我认为probleme的存储过程。

string search = "julien"; 
      var list = db.Users.Where(x => x.Name.StartsWith(search)); 
      string query = list.ToString(); 

=> SELECT [Extent1] [用户ID] AS [用户ID]， [Extent1]。[名称] AS [名称] FROM [DBO]。[用户] AS [Extent1] WHERE [Extent1]。[名称] LIKE @ p__linq__0 ESCAPE N '〜'

var list2 = db.Users.Where(x => x.Name.StartsWith("julien")); 
      string query2 = list2.ToString(); 

=> SELECT [Extent1] [用户ID] AS [用户ID]， [Extent1]。[名称] AS [名称] FROM [dbo]。[Users] AS [Extent1] WHERE [Extent1]。[Name] LIKE N'julien％'

因此，如果我在查询中使用变量获取存储过程，如果使用const我得到选择。

在存储过程（由实体产生）使得出现@ p__linq__0所以加ESCAPE N '〜' 避免wildCaractere在变量。

所以现在的问题是简单的。如何避免与变量查询？这是可能的 ？ 谢谢

Answer 1

因此，您需要做的是取一个变量的值，并将其用作正在生成的Expression中的常量。这实际上很有可能。我们需要的是一个表达式，它接受你想要的参数作为你实际选择器的参数，作为第二个参数，它是常量值的占位符，然后是你想成为常量的值。然后，我们可以替换常量的值参数的所有实例，仅留下了真正的参数映射到结果的函数：

public static Expression<Func<TSource, TResult>> EmbedConstant 
    <TSource, TResult, TConstant>(
    this Expression<Func<TSource, TConstant, TResult>> expression, 
    TConstant constant) 
{ 
    var body = expression.Body.Replace(
     expression.Parameters[1], 
     Expression.Constant(constant)); 
    return Expression.Lambda<Func<TSource, TResult>>(
     body, expression.Parameters[0]); 
} 

这依赖于下列的方法来与更换一个表达的所有实例另：

public static Expression Replace(this Expression expression, 
    Expression searchEx, Expression replaceEx) 
{ 
    return new ReplaceVisitor(searchEx, replaceEx).Visit(expression); 
} 
internal class ReplaceVisitor : ExpressionVisitor 
{ 
    private readonly Expression from, to; 
    public ReplaceVisitor(Expression from, Expression to) 
    { 
     this.from = from; 
     this.to = to; 
    } 
    public override Expression Visit(Expression node) 
    { 
     return node == from ? to : base.Visit(node); 
    } 
} 

这允许你映射这样的：

string search = "julien"; 
var list = db.Users.Where(x => x.Name.StartsWith(search)); 
string query = list.ToString(); 

进入这个：

string search = "julien"; 
Expression<Func<User, string, bool>> predicate = 
    (item, searchTerm) => item.Name.StartsWith(searchTerm); 
var list = db.Users.Where(predicate.EmbedConstant(search)); 
string query = list.ToString();