DBNull F# snippet (#7598)

Author: albert-du

samples/snippets/fsharp/VS_Snippets_CLR_System/system.DBNull.Class/fs/DBNullExamples.fs

@@ -0,0 +1,62 @@
+open System
+open System.Data
+open System.Data.OleDb
+
+type DBNullExample() =
+    // <Snippet1>
+    member this.OutputLabels(dt: DataTable) =
+        let mutable label = ""
+
+        // Iterate rows of table
+        for row in dt.Rows do
+            let mutable label = String.Empty
+            label <- label + this.AddFieldValue(label, row, "Title")
+            label <- label + this.AddFieldValue(label, row, "FirstName")
+            label <- label + this.AddFieldValue(label, row, "MiddleInitial")
+            label <- label + this.AddFieldValue(label, row, "LastName")
+            label <- label + this.AddFieldValue(label, row, "Suffix")
+            label <- label + "\n"
+            label <- label + this.AddFieldValue(label, row, "Address1")
+            label <- label + this.AddFieldValue(label, row, "AptNo")
+            label <- label + "\n"
+            let labelLen = label.Length
+            label <- label + this.AddFieldValue(label, row, "Address2")
+            let labelLen =
+                if label.Length <> labelLen then
+                    label + "\n"
+                else label
+            label <- label + this.AddFieldValue(label, row, "City")
+            label <- label + this.AddFieldValue(label, row, "State")
+            label <- label + this.AddFieldValue(label, row, "Zip")
+            printfn $"{label}"
+            printfn ""
+
+    member _.AddFieldValue(label: string, row: DataRow, fieldName: string) =
+        if DBNull.Value.Equals row[fieldName] |> not then
+            (string row[fieldName]) + " "
+        else
+            String.Empty
+    // </Snippet1>
+
+let ex = DBNullExample()
+let conn = new OleDbConnection()
+let cmd = new OleDbCommand()
+let adapter = new OleDbDataAdapter()
+let ds = new DataSet()
+let dbFilename = @"c:\Data\contacts.mdb"
+
+// Open database connection
+conn.ConnectionString <- "Provider=Microsoft.Jet.OLEDB.4.0Data Source=" + dbFilename + ""
+conn.Open()
+// Define command : retrieve all records in contact table
+cmd.CommandText <- "SELECT * FROM Contact"
+cmd.Connection <- conn
+adapter.SelectCommand <- cmd
+// Fill dataset
+ds.Clear()
+adapter.Fill(ds, "Contact")
+|> ignore
+// Close connection
+conn.Close()
+// Output labels to console	
+ex.OutputLabels ds.Tables["Contact"]

samples/snippets/fsharp/VS_Snippets_CLR_System/system.DBNull.Class/fs/fs.fsproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="System.Data.OleDb" Version="6.0.0" />
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="DBNullExamples.fs" />
+  </ItemGroup>
+</Project>

xml/System/DBNull.xml

@@ -85,6 +85,7 @@
  The following example calls the `DBNull.Value.Equals` method to determine whether a database field in a contacts database has a valid value. If it does, the field value is appended to the string output in a label.  
   
  :::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.DBNull.Class/cs/DBNullExamples.cs" id="Snippet1":::
+ :::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR_System/system.DBNull.Class/fs/DBNullExamples.fs" id="Snippet1":::
  :::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.DBNull.Class/vb/DBNullExamples.vb" id="Snippet1":::  
   
  ]]></format>
@@ -1133,6 +1134,7 @@
  The following example calls the `DBNull.Value.Equals` method to determine whether a database field in a contacts database has a valid value. If it does, the field value is appended to the string output in a label.  
   
  :::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.DBNull.Class/cs/DBNullExamples.cs" id="Snippet1":::
+ :::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR_System/system.DBNull.Class/fs/DBNullExamples.fs" id="Snippet1":::
  :::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.DBNull.Class/vb/DBNullExamples.vb" id="Snippet1":::  
   
  ]]></format>