Inspect database schemas and execute SQL queries across multiple database providers with LINQ to DB.
io.github.linq2db/linq2db.cli — Model Context Protocol (MCP) Server
The io.github.linq2db/linq2db.cli MCP server inspects database schemas and executes SQL queries across multiple database providers using LINQ to DB. It provides a CLI-oriented interface for working with database metadata and running SQL, based on the server’s stated description.
🛠️ Key Features
Inspect database schemas
Execute SQL queries
Support multiple database providers
Uses LINQ to DB
🚀 Use Cases
Reviewing schema information across different database systems
Running SQL queries against multiple database providers via LINQ to DB
⚡ Developer Benefits
Query execution and schema inspection across providers from one tooling surface
Integration path via LINQ to DB as described by the server
⚠️ Limitations
No additional constraints, tool list details, or operational limits were provided in the available source data
LINQ to DB is the fastest LINQ database access library offering a simple, light, fast, and type-safe layer between your POCOs and your database.
Architecturally it is one step above micro-ORMs like Dapper, Massive, or PetaPoco, in that you work with LINQ expressions, not with magic strings, while maintaining a thin abstraction layer between your code and the database. Your queries are checked by the C# compiler and allow for easy refactoring.
However, it's not as heavy as LINQ to SQL or Entity Framework. There is no change-tracking, so you have to manage that yourself, but on the positive side you get more control and faster access to your data.
In other words LINQ to DB is type-safe SQL.
LINQ to DB also very nice for F# developers (see Tests/FSharp and Source/LinqToDB.FSharp project for details).
You can simply pass connection string into DataConnection or DataContext constructor using DataOptions class.
Minimal configuration example:
cs
var db = new DataConnection(
new DataOptions()
.UseSqlServer(@"Server=.\;Database=Northwind;Trusted_Connection=True;"));
Use connection configuration action to setup SqlClient-specific authentication token:
cs
var options = new DataOptions()
.UseSqlServer(connectionString, SqlServerVersion.v2017, SqlServerProvider.MicrosoftDataSqlClient)
.UseBeforeConnectionOpened(cn =>
{
((SqlConnection)cn).AccessToken = accessToken;
});
// pass configured options to data context constructorvar dc = new DataContext(options);
TIP
There are a lot of configuration methods on DataOptions you can use.
TIP
It is recommended to create configured DataOptions instance once and use it everywhere. E.g. you can register it in your DI container.
Using Config File (.NET Framework)
In your web.config or app.config make sure you have a connection string (check this file for supported providers):
You can generate POCO classes from your database using linq2db.clidotnet tool.
Alternatively, you can write them manually and map to database using mapping attributes or fluent mapping configuration. Also you can use POCO classes as-is without additional mappings if they use same naming for classes and properties as table and column names in database.
Configuration using mapping attributes
code
using System;
using LinqToDB.Mapping;
[Table("Products")]
public class Product
{
[PrimaryKey, Identity]
public int ProductID { get; set; }
[Column("ProductName"), NotNull]
public string Name { get; set; }
[Column]
public int VendorID { get; set; }
[Association(ThisKey = nameof(VendorID), OtherKey=nameof(Vendor.ID))]
public Vendor Vendor { get; set; }
// ... other columns ...
}
This approach involves attributes on all properties that should be mapped. This way lets you to configure all possible things linq2db ever supports. There is one thing to mention: if you add at least one attribute into POCO, all other properties should also have attributes, otherwise they will be ignored:
code
using System;
using LinqToDB.Mapping;
[Table("Products")]
public class Product
{
[PrimaryKey, Identity]
public int ProductID { get; set; }
// Property `Name` will be ignored as it lacks `Column` attibute.
public string Name { get; set; }
}
Fluent Configuration
This method lets you configure your mapping dynamically at runtime. Furthermore, it lets you to have several different configurations if you need so. You will get all configuration abilities available with attribute configuration. These two approaches are interchangeable in their abilities. This kind of configuration is done through the class MappingSchema.
With Fluent approach you can configure only things that require it explicitly. All other properties will be inferred by linq2db:
code
// IMPORTANT: configure mapping schema instance only once
// and use it with all your connections that need those mappings
// Never create new mapping schema for each connection as
// it will seriously harm performance
var myFluentMappings = new MappingSchema();
var builder = new FluentMappingBuilder(mappingSchema);
builder.Entity<Product>()
.HasTableName("Products")
.HasSchemaName("dbo")
.HasIdentity(x => x.ProductID)
.HasPrimaryKey(x => x.ProductID)
.Ignore(x => x.SomeNonDbProperty)
.Property(x => x.TimeStamp)
.HasSkipOnInsert()
.HasSkipOnUpdate()
.Association(x => x.Vendor, x => x.VendorID, x => x.VendorID, canBeNull: false)
;
//... other mapping configurations
// commit configured mappings to mapping schema
builder.Build();
In this example we configured only three properties and one association. We let Linq To DB to infer all other properties as columns with same name as property.
To use your MappingSchema instance you should pass it DataConnection or DataContext constructor:
cs
var options = new DataOptions()
.UseSqlServer(@"Server=.\;Database=Northwind;Trusted_Connection=True;")
.UseMappingSchema(myFluentMappings);
var db = new DataConnection(option);
Inferred Configuration
This approach involves no attributes at all. In this case Linq To DB will use POCO's name as table name and property names as column names (with exact same casing, which could be important for case-sensitive databases). This might seem to be convenient, but there are some restrictions:
Linq To DB will not infer primary key even if class has property called ID;
it will not infer nullability of reference types if you don't use nullable reference types annotations;
associations will not be automatically configured.
code
using System;
public class Product
{
public int ProductID { get; set; }
public string Name { get; set; }
public int VendorID { get; set; }
public Vendor Vendor { get; set; }
// ... other columns ...
}
This way Linq To DB will auto-configure Product class to map to Product table with fields ProductID, Name, and VendorID. POCO will not get ProductID property treated as primary key. And there will be no association with Vendor.
This approach is not generally recommended.
DataConnection class
At this point LINQ to DB doesn't know how to connect to our database or which POCOs go with what database. All this mapping is done through a DataConnection class:
code
public class DbNorthwind : LinqToDB.Data.DataConnection
{
public DbNorthwind() : base("Northwind") { }
public ITable<Product> Product => this.GetTable<Product>();
public ITable<Category> Category => this.GetTable<Category>();
// ... other tables ...
}
We call the base constructor with the "Northwind" parameter. This parameter (called configuration name) has to match the name="Northwind" we defined above as name of our connection string. We also added convenience properties for Product and Category mapping classes to write LINQ queries.
And now let's get some data:
cs
using LinqToDB;
publicstatic List<Product> GetProducts()
{
usingvar db = new DbNorthwind();
var query = from p in db.Product
where p.ProductID > 25orderby p.Name descendingselect p;
return query.ToList();
}
Make sure you always wrap your DataConnection class (in our case DbNorthwind) in a using statement. This is required for proper resource management, like releasing the database connections back into the pool (more details).
Queries
Selecting Columns
Most times we get the entire row from the database:
code
from p in db.Product
where p.ProductID == 5
select p;
However, sometimes getting all the fields is too wasteful so we want only certain fields, but still use our POCOs; something that is challenging for libraries that rely on object tracking, like LINQ to SQL.
code
from p in db.Product
orderby p.Name descending
select new Product
{
Name = p.Name
};
Composing queries
Rather than concatenating strings we can 'compose' LINQ expressions. In the example below the final SQL will be different if onlyActive is true or false, or if searchFor is not null.
code
public static Product[] GetProducts(bool onlyActive, string searchFor)
{
using var db = new DbNorthwind();
var products = from p in db.Product
select p;
if (onlyActive)
{
products = from p in products
where !p.Discontinued
select p;
}
if (searchFor != null)
{
products = from p in products
where p.Name.Contains(searchFor)
select p;
}
return products.ToArray();
}
Paging
A lot of times we need to write code that returns only a subset of the entire dataset. We expand on the previous example to show what a product search function could look like.
Keep in mind that the code below will query the database twice. Once to find out the total number of records, something that is required by many paging controls, and once to return the actual data.
code
public static List<Product> Search(
string searchFor,
int currentPage,
int pageSize,
out int totalRecords)
{
using var db = new DbNorthwind();
var products = from p in db.Product
select p;
if (searchFor != null)
{
products = from p in products
where p.Name.Contains(searchFor)
select p;
}
totalRecords = products.Count();
return products.Skip((currentPage - 1) * pageSize).Take(pageSize).ToList();
}
Joins
This assumes we added a Category class, just like we did with the Product class, defined all the fields, and defined table access property in our DbNorthwind data access class. We can now write an INNER JOIN query like this:
code
from p in db.Product
join c in db.Category on p.CategoryID equals c.CategoryID
select new Product
{
Name = p.Name,
Category = c
};
and a LEFT JOIN query like this:
code
from p in db.Product
from c in db.Category.Where(q => q.CategoryID == p.CategoryID).DefaultIfEmpty()
select new Product
{
Name = p.Name,
Category = c
};
In the previous example we assign an entire Category object to our product, but what if we want all the fields in our Product class, but we don't want to specify every field by hand? Unfortunately, we cannot write this:
code
from p in db.Product
from c in db.Category.Where(q => q.CategoryID == p.CategoryID).DefaultIfEmpty()
select new Product(c);
The query above assumes the Product class has a constructor that takes in a Category object. The query above won't work, but we can work around that with the following query:
code
from p in db.Product
from c in db.Category.Where(q => q.CategoryID == p.CategoryID).DefaultIfEmpty()
select Product.Build(p, c);
For this to work, we need a function in the Product class that looks like this:
code
public static Product Build(Product? product, Category category)
{
if (product != null)
{
product.Category = category;
}
return product;
}
One caveat with this approach is that if you're using it with composed queries (see example above) the select Build part has to come only in the final select.
Insert
At some point we will need to add a new Product to the database. One way would be to call the Insert extension method found in the LinqToDB namespace; so make sure you import that.
code
using LinqToDB;
using var db = new DbNorthwind();
db.Insert(product);
This inserts all the columns from our Product class, but without retrieving the generated identity value. To do that we can use InsertWith*Identity methods, like this:
code
using LinqToDB;
using var db = new DbNorthwind();
product.ProductID = db.InsertWithInt32Identity(product);
There is also InsertOrReplace that updates a database record if it was found by primary key or adds it otherwise.
If you need to insert only certain fields, or use values generated by the database, you could write:
code
using LinqToDB;
using var db = new DbNorthwind();
db.Product
.Value(p => p.Name, product.Name)
.Value(p => p.UnitPrice, 10.2m)
.Value(p => p.Added, () => Sql.CurrentTimestamp)
.Insert();
Use of this method also allows us to build insert statements like this:
code
using LinqToDB;
using var db = new DbNorthwind();
var statement = db.Product
.Value(p => p.Name, product.Name)
.Value(p => p.UnitPrice, 10.2m);
if (storeAdded) statement.Value(p => p.Added, () => Sql.CurrentTimestamp);
statement.Insert();
Update
Updating records follows similar pattern to Insert. We have an extension method that updates all the columns in the database:
code
using LinqToDB;
using var db = new DbNorthwind();
db.Update(product);
And we also have a lower level update mechanism:
code
using LinqToDB;
using var db = new DbNorthwind();
db.Product
.Where(p => p.ProductID == product.ProductID)
.Set(p => p.Name, product.Name)
.Set(p => p.UnitPrice, product.UnitPrice)
.Update();
Similarly, we can break an update query into multiple pieces if needed:
code
using LinqToDB;
using var db = new DbNorthwind();
var statement = db.Product
.Where(p => p.ProductID == product.ProductID)
.Set(p => p.Name, product.Name);
if (updatePrice) statement = statement.Set(p => p.UnitPrice, product.UnitPrice);
statement.Update();
You're not limited to a single record update. For example, we could discontinue all the products that are no longer in stock:
code
using LinqToDB;
using var db = new DbNorthwind();
db.Product
.Where(p => p.UnitsInStock == 0)
.Set(p => p.Discontinued, true)
.Update();
Delete
Similar to how you update records, you can also delete records:
code
using LinqToDB;
using var db = new DbNorthwind();
db.Product
.Where(p => p.Discontinued)
.Delete();
Bulk Copy
Bulk copy feature supports the transfer of large amounts of data into a table from another data source. For more details read this article.
code
using LinqToDB.Data;
[Table("ProductsTemp")]
public class ProductTemp
{
[PrimaryKey]
public int ProductID { get; set; }
[Column("ProductName"), NotNull]
public string Name { get; set; }
// ... other columns ...
}
var list = new List<ProductTemp>();
// ... populate list ...
using var db = new DbNorthwind();
db.BulkCopy(list);
Transactions
Using database transactions is easy. All you have to do is call BeginTransaction() on your DataConnection, run one or more queries, and then commit the changes by calling CommitTransaction(). If something happened and you need to roll back your changes you can either call RollbackTransaction() or throw an exception.
code
using var db = new DbNorthwind();
db.BeginTransaction();
// or
//using var tr = db.BeginTransaction();
// ... select / insert / update / delete ...
if (somethingIsNotRight)
{
db.RollbackTransaction();
// or
// tr.Rollback();
}
else
{
db.CommitTransaction();
// or
// tr.Commit();
}
Also, you can use .NET built-in TransactionScope class:
code
using var transaction = new TransactionScope();
// or for async code
// using var transaction = new TransactionScope(TransactionScopeAsyncFlowOption.Enabled);
using var db = new DbNorthwind();
...
transaction.Complete();
It should be noted that there are two base classes for your "context" class: LinqToDB.Data.DataConnection and LinqToDB.DataContext. The key difference between them is in connection retention behaviour. DataConnection opens connection with first query and holds it open until dispose happens. DataContext behaves the way you might used to with Entity Framework: it opens connection per query and closes it right after query is done.
This difference in behavior matters when used with TransactionScope:
code
using var db = new LinqToDB.Data.DataConnection("provider name", "connection string");
var product = db.GetTable<Product>()
.FirstOrDefault(); // connection opened here
var scope = new TransactionScope();
// this transaction was not attached to connection
// because it was opened earlier
product.Name = "Lollipop";
db.Update(product);
scope.Dispose();
// no transaction rollback happed, "Lollipop" has been saved
A DataConnection is attached with ambient transaction in moment it is opened. Any TransactionScopes created after the connection is created will no effect on that connection. Replacing DataConnection with DataContext in code shown earlier will make transaction scope work as expected: the created record will be discarded with the transaction.
Although, DataContext appears to be the right class to choose, it is strongly recommended to use DataConnection instead. It's default behaviour might be changed with setting CloseAfterUse property to true:
code
public class DbNorthwind : LinqToDB.Data.DataConnection
{
public DbNorthwind() : base("Northwind")
{
(this as IDataContext).CloseAfterUse = true;
}
}
Here you can read about Window (Analytic) Functions support.
MiniProfiler
If you would like to use MiniProfiler or other profiling tool that wraps ADO.NET provider classes, you need to configure our regular DataConnection to use wrapped connection.
code
// example of SQL Server-backed data connection with MiniProfiler enabled for debug builds
public class DbDataContext : DataConnection
{
// let's use profiler only for debug builds
#if !DEBUG
// regular non-profiled constructor
public DbDataContext() : base("Northwind") {}
#else
public DbDataContext()
: base(
new DataOptions()
.UseSqlServer(connectionString, SqlServerVersion.v2012)
.UseConnectionFactory(GetConnection)
.UseInterceptor(new UnwrapProfilerInterceptor()))
{
}
// wrap connection into profiler wrapper
private static DbConnection GetConnection(DataOptions options)
{
// create provider-specific connection instance. SqlConnection in our case
var dbConnection = new SqlConnection(options.ConnectionOptions.ConnectionString);
// wrap it by profiler's connection implementation
return new StackExchange.Profiling.Data.ProfiledDbConnection(
dbConnection,
MiniProfiler.Current);
}
// define UnwrapDataObjectInterceptor
sealed class UnwrapProfilerInterceptor : UnwrapDataObjectInterceptor
{
public override DbConnection UnwrapConnection(IDataContext dataContext, DbConnection connection)
{
return connection is ProfiledDbConnection c ? c.WrappedConnection : connection;
}
public override DbTransaction UnwrapTransaction(IDataContext dataContext, DbTransaction transaction)
{
return transaction is ProfiledDbTransaction t ? t.WrappedTransaction : transaction;
}
public override DbCommand UnwrapCommand(IDataContext dataContext, DbCommand command)
{
return command is ProfiledDbCommand c ? c.WrappedCommand : command;
}
public override DbDataReader UnwrapDataReader(IDataContext dataContext, DbDataReader dataReader)
{
return dataReader is ProfiledDbDataReader dr ? dr.WrappedReader : dataReader;
}
}
#endif
}
F#
Sample query with load child relations
fsharp
let getPerson (db: IDataContext) (id: int) =
let persons = db.GetTable<Person>().LoadWith(fun x -> x.Patient)
let person =
query {
for p in persons do
where (p.ID = id)
exactlyOne
}
person
