linq to sql startwith性能索引列

Question

我首先使用实体​​代码。索引列：

• SourceCatalogId
• Disabled
• CategoryPath

表中的4万行

我的问题是查询需要40秒钟！

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();

通过sql profiler进行的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where子句中的最后一个子句中，如果我在以下位置删除“ scape N”〜“ ”：

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

查询需要4秒。

正常吗？索引用途？我如何用startWith解决呢？

编辑

categoryPath的索引属性：

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

编辑2

好的，我非常接近，我认为问题是存储过程。

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

=> SELECT [Extent1].[UserId] AS [UserId], [Extent1].[Name] AS [Name] FROM [dbo].[Users] AS [Extent1] WHERE [Extent1].[Name] LIKE @p__linq__0 ESCAPE N’~’

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

=> SELECT [Extent1].[UserId] AS [UserId], [Extent1].[Name] AS [Name] 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，则如果我使用const则获取选择。

在存储过程中（由实体生成）使 @ p__linq__0 出现，因此 在变量中添加 ESCAPE N’〜 ‘
以避免wildCaractere。

因此，现在的问题更为简单。如何避免使用变量查询？这是可能的 ？谢谢

Answer 1

因此，这里您需要做的是获取变量的值，并将其用作Expression要生成的变量中的常量。实际上这是完全有可能的。我们需要的是一个表达式，该表达式接受您想要的参数作为实选择器的参数，作为第二个参数，该第二个参数是常量值的占位符，然后是您想要成为常量的值。然后，我们可以用常量的值替换参数的所有实例，只剩下一个将真实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]);
}

这依靠以下方法将一个表达式的所有实例替换为另一个表达式：

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);
    }
}

这使您可以对此进行映射：

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

变成这个：

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();