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Jan 18, 2022
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System.DBNull F# snippet #7598

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62 changes: 62 additions & 0 deletions samples/snippets/fsharp/VS_Snippets_CLR_System/system.DBNull.Class/fs/DBNullExamples.fs
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@@ -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"]
12 changes: 12 additions & 0 deletions samples/snippets/fsharp/VS_Snippets_CLR_System/system.DBNull.Class/fs/fs.fsproj
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<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>
2 changes: 2 additions & 0 deletions xml/System/DBNull.xml
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Expand Up @@ -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>
Expand Down Expand Up @@ -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>
Expand Down