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我有一个包含 3 个表的数据库

产品表 供应商表 类别表
身份证 身份证 身份证
产品名称 供应商名称 类别名称
数量 。.
供应商 ID。.
类别 ID
.
.

我正在使用 PredicateBuilder 根据所选产品字段（数量、产品名称 ...）选择产品 我如何使用 PredicateBuilder 或任何其他方法根据其供应商名称或类别名称选择产品

请我使用 VB.NET 我看到了很多 C# 示例，但我无法理解或翻译它我正在考虑在 predicateBuilder 中使用 join 但我不知道如何！！！！

为了更清楚，我想要的是在一次搜索中组合多个字段，例如：

给我一个名称包含“s”且数量 <10 且供应商名称为 Kimo 的产品

给我一个我的名字只包含“g”的产品

给我类别名称“机器”的产品

.

.

而且这个搜索谓词是可变的，因为每个 Products 表都有很多字段，所以搜索是根据所选字段动态搜索的

等待您的热心帮助。

我认为 Arion 的答案是正确的，但它需要一些修改无论如何我想出了这个解决方案，它不是最有效的一个，但它解决了我的问题。

 Dim SupplierAlso As String = ""
 Dim CategoryAlso As String = ""
 Dim pred = PredicateBuilder.True(Of Products)()
 Select Case Entry
                        Case "Number"
                            Dim Inum = Entry
                            pred = pred.And(Function(m As products) m.ID.Equals(CInt(Inum)))

                        Case "ProductName"

                            Dim IName = Entry
                            pred = pred.And(Function(m As Products) m.ProductName.IndexOf(IName, StringComparison.OrdinalIgnoreCase) >= 0)

. . . 案例“供应商”

                            SupplierAlso = Entry

                        Case "Category"

                            CategoryAlso = Ent

下一个

            Dim f As ProductsDataTable = Products.Product
            Dim tmp As IEnumerable(Of Products) = New ProductsDataTable().AsEnumerable()
            tmp = f.AsEnumerable.Where(pred.Compile)


            Dim qry

             If CategoryAlso = "" And SupplierAlso = "" Then
                q = (From prods In tmp
                      Join Cats In Categories
                      On prods.CategoryId Equals Cats.ID
                      Join Supps In Suppliers
                      On Supps.ID Equals prods.SupplierId
                      Select Supps.SupplierName, Cats.CategoryName, prods.ID _ 
                      , prods.ProductName,   prods.UnitPrice, prods.CategoryId _ 
                      , prods.SupplierId, prods.Location, _
                      prods.Description, prods.SellPrice, prods.CountInStock _ 
                      , prods.ProductionDate, prods.ExpiryDate, _
                      prods.ProductType, prods.ProductSeason).ToList

            ElseIf CategoryAlso <> "" And SupplierAlso <> "" Then

                q = (From prods In tmp
                      Join Cats In Categories
                      On prods.CategoryId Equals Cats.ID
                       Join Supps In Suppliers
                       On Supps.ID Equals prods.SupplierId
                       Where Cats.CategoryName.IndexOf((CategoryAlso)  
                 ,  StringComparison.OrdinalIgnoreCase) >= 0 And _                                Supps.SupplierName.IndexOf((SupplierAlso), _ 
                      StringComparison.OrdinalIgnoreCase) >= 0
                      Select Supps.SupplierName, Cats.CategoryName, prods.ID, _  
                     prods.ProductName, prods.UnitPrice, prods.CategoryId, _ 
                     prods.SupplierId, prods.Location, _
                      prods.Description, prods.SellPrice, prods.CountInStock,  _ 
                      prods.ProductionDate, prods.ExpiryDate, _
                      prods.ProductType, prods.ProductSeason).ToList

            ElseIf SupplierAlso <> "" And CategoryAlso = "" Then

                q = (From prods In tmp
                        Join Cats In Categories
                        On Cats.ID Equals prods.CategoryId
                        Join Supps In Suppliers
                        On prods.SupplierId Equals Supps.ID Where _ 
                         Supps.SupplierName.IndexOf((SupplierAlso),  _ 
                         StringComparison.OrdinalIgnoreCase) >= 0
                        Select Cats.CategoryName, Supps.SupplierName, prods.ID,  _ 
                        prods.ProductName, prods.UnitPrice, prods.CategoryId, _ 
                        prods.SupplierId, prods.Location, _
                        prods.Description, prods.SellPrice, prods.CountInStock, _  
                        prods.ProductionDate, prods.ExpiryDate, _
                        prods.ProductType, prods.ProductSeason).ToList

            ElseIf CategoryAlso <> "" And SupplierAlso = "" Then

                q = (From prods In tmp
                        Join Cats In Categories
                        On prods.CategoryId Equals Cats.ID Where Cats.CategoryName.IndexOf _ 
                        ((CategoryAlso), StringComparison.OrdinalIgnoreCase) >= 0
                        Join Supps In Suppliers On Supps.ID Equals prods.SupplierId
                        Select Supps.SupplierName, Cats.CategoryName, prods.ID, _ 
                        prods.ProductName, prods.UnitPrice, prods.CategoryId, _ 
                        prods.SupplierId, prods.Location, _
                        prods.Description, prods.SellPrice, prods.CountInStock, _ 
                        prods.ProductionDate, prods.ExpiryDate, _
                        prods.ProductType, prods.ProductSeason).ToList

            End If

For Each it In q With it

                    DataGridView2.Rows.Add _ 
                   ({.ID, .ProductName, .UnitPrice, .categoryname, .suppliername, .Location, _
                                            .Description, .SellPrice, .CountInStock, _                                                .ProductionDate, .ExpiryDate, _
                                            .ProductType, .ProductSeason})

                End With

            Next

那么你认为，有没有更好的方法？当然是的？愚蠢的问题，但是在哪里？

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1 回答 1

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所以我会做这样的事情。我已经简化了 where 语句，但我想你会明白我的意思：

dim checkCategoryName as boolean=true
dim checkSupplier as boolean=true
dim checkQuantity as boolean=true
dim query= db.Products.Select (function(p) p)
if checkCategoryName then
    query=query _ 
            .Where (function(p) db.Categories.Where (function(c) c.CategoryName="??" ) _ 
            .Select (function(c) c.Id) _ 
            .Contains(p.CategoryId))
end if
if checkSupplier then
    query=query _ 
            .Where (function(q) db.Suppliers.Where (function(s) s.SupplierName="??") _ 
            .Select (function(s) s.Id) _ 
            .Contains(q.SupplierId))
end if
if checkQuantity then
    query=query.Where (function(q) q.Quantity<10)
end if
dim result=query.ToList()

其中 db 是 linq 数据上下文。

于 2012-02-06T10:04:50.267 回答