Implements DbfDbConnection. (#258)

* Implements DbfDbConnection.

Thanks to @TonyValenti for the contributions.

* Simplifies QueryParser and adds unit tests

* Simplifies DbfDbCommand.ExecuteDbDataReader

* Code tidy

* Updates README.md

Author: chrisrichards

DbfDataReader.sln

@@ -6,6 +6,9 @@ MinimumVisualStudioVersion = 10.0.40219.1
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{02A96866-FEA4-483E-A6FD-CB8660F51FD3}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{8C65E3B7-6E4F-470A-9422-7B273FE6EBF6}"
+	ProjectSection(SolutionItems) = preProject
+		README.md = README.md
+	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "test", "test", "{6E1D36E2-2D05-4ACF-80B7-1AFB75A20839}"
 EndProject

README.md

@@ -105,6 +105,48 @@ using (var dbfDataReader = new DbfDataReader(dbfPath, options))
 }
 ```
 
+There is also an implementation of DbConnection so you can query a folder of files e.g.
+
+```csharp
+var dbConnection = new DbfDbConnection(string.Empty, string.Empty);
+dbConnection.ConnectionString = $"Folder=./test/fixtures;SkipDeletedRecords=false";
+dbConnection.Open();
+
+var dbCommand = dbConnection.CreateCommand();
+dbCommand.CommandText = "select * from dbase_03.dbf;";
+
+var reader = await dbCommand.ExecuteReaderAsync();
+while (await reader.ReadAsync())
+{
+    var valueCol1 = reader.GetString(0);
+    var valueCol11 = reader.GetDecimal(10);
+}
+```
+
+The connection string supports the options available in `DbfDataReaderOptions`:
+
+- Folder - the folder containing the files to be queried
+  - required
+  - string
+- Encoding - the encoding to be used
+  - optional
+  - string
+  - valid Encoding name from [Encoding](https://learn.microsoft.com/en-us/dotnet/api/System.Text.Encoding)
+- ReadFloatsAsDecimals - whether to read floats as decimals
+  - optional
+  - boolean
+  - defaults to false
+- SkipDeletedRecords - whether to skip deleted records
+  - optional
+  - boolean
+  - defaults to true
+- StringTrimming - string timming behaviour
+  - optional
+  - string
+  - defaults to 'None'
+  - one of 'None', 'Trim', 'TrimStart', 'TrimEnd'
+
+
 Used by 
 
 - DbfBulkCopy

src/DbfDataReader/DbfDataReader.csproj

@@ -20,6 +20,10 @@
     <MinVerTagPrefix>v</MinVerTagPrefix>
   </PropertyGroup>
 
+  <ItemGroup>
+    <InternalsVisibleTo Include="DbfDataReader.Tests" />
+  </ItemGroup>
+  
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="10.0.103" PrivateAssets="All" />
     <PackageReference Include="MinVer" Version="7.0.0" PrivateAssets="All" />

src/DbfDataReader/DbfDbCommand.cs

@@ -0,0 +1,74 @@
+using System;
+using System.Data;
+using System.Data.Common;
+using System.IO;
+
+namespace DbfDataReader
+{
+    public class DbfDbCommand : DbCommand
+    {
+        public override string CommandText { get; set; }
+        public override int CommandTimeout { get; set; }
+        public override CommandType CommandType { get; set; }
+        public override bool DesignTimeVisible { get; set; }
+        public override UpdateRowSource UpdatedRowSource { get; set; }
+        protected override DbConnection DbConnection { get; set; }
+        protected override DbParameterCollection DbParameterCollection { get; }
+        protected override DbTransaction DbTransaction { get; set; }
+
+        public override void Cancel()
+        {
+            throw new NotImplementedException();
+        }
+
+        public override int ExecuteNonQuery()
+        {
+            throw new NotImplementedException();
+        }
+
+        public override object ExecuteScalar()
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void Prepare()
+        {
+            throw new NotImplementedException();
+        }
+
+        protected override DbParameter CreateDbParameter()
+        {
+            throw new NotImplementedException();
+        }
+
+        protected override DbDataReader ExecuteDbDataReader(CommandBehavior behavior)
+        {
+            var dbfDbConnection = Connection as DbfDbConnection;
+            if (dbfDbConnection is null)
+            {
+                throw new InvalidOperationException($"{nameof(DbfDbConnection)} is not available");
+            }
+
+            var folder = dbfDbConnection.Database;
+            if (string.IsNullOrWhiteSpace(folder))
+            {
+                throw new DirectoryNotFoundException("No folder was specified for the Dbf files.");
+            }
+            
+            if (!Directory.Exists(folder))
+            {
+                throw new DirectoryNotFoundException($"The specified folder does not exist: {folder}");
+            }
+            
+            var fileName = QueryParser.Parse(CommandText);
+            var filePath = Path.Combine(folder, $"{fileName}");
+            if (!File.Exists(filePath))
+            {
+                throw new FileNotFoundException(filePath);
+            }
+
+            var options = dbfDbConnection.Options;
+            return new DbfDataReader(filePath, options);
+        }
+    }
+}

src/DbfDataReader/DbfDbConnection.cs

@@ -0,0 +1,88 @@
+using System;
+using System.Data;
+using System.Data.Common;
+using System.IO;
+
+namespace DbfDataReader
+{
+    public class DbfDbConnection : DbConnection
+    {
+        private string _database = string.Empty;
+        private ConnectionState _state  = ConnectionState.Closed;
+
+        public DbfDbConnection(string dataSource, string serverVersion)
+        {
+            DataSource = dataSource;
+            ServerVersion = serverVersion;
+        }
+
+        public DbfDataReaderOptions Options { get; private set; } = new DbfDataReaderOptions();
+
+        public override string ConnectionString { get; set; }
+        public override string DataSource { get; }
+        public override string ServerVersion { get; }
+        
+        public override ConnectionState State => _state;
+        public override string Database => _database;
+        
+        public override void ChangeDatabase(string databaseName)
+        {
+            if (!Directory.Exists(databaseName))
+            {
+                throw new DirectoryNotFoundException(databaseName);
+            }
+            
+            _database = databaseName;
+        }
+
+        public override void Close()
+        {
+            _state = ConnectionState.Closed;
+        }
+
+        public override void Open()
+        {
+            var builder = new DbfDbConnectionStringBuilder(ConnectionString);
+
+            ChangeDatabase(builder.Folder);
+
+            var options = new DbfDataReaderOptions();
+            
+            if (builder.Encoding is var encoding) 
+            {
+                options.Encoding = encoding;
+            }
+
+            if (builder.ReadFloatsAsDecimals is var readFloatsAsDecimals)
+            {
+                options.ReadFloatsAsDecimals = readFloatsAsDecimals;
+            }
+
+            if (builder.SkipDeletedRecords is var skipDeletedRecords) 
+            {
+                options.SkipDeletedRecords = skipDeletedRecords;
+            }
+
+            if (builder.StringTrimming is var stringTrimming)
+            {
+                options.StringTrimming = stringTrimming;
+            }
+
+            Options = options;
+            _state = ConnectionState.Open;
+        }
+
+        protected override DbTransaction BeginDbTransaction(IsolationLevel isolationLevel)
+        {
+            throw new NotImplementedException();
+        }
+
+        protected override DbCommand CreateDbCommand()
+        {
+            return new DbfDbCommand
+            {
+                Connection = this,
+            };
+        }
+    }
+}