CODEWITHSUNDEEP
c#sqlef-code-firstentity-framework-4.1
0xbadf00d
0xbadf00d

Reputation: 18178

Entity Framework - How to check if table exists?

I'm using the Entity Framework with Code First approach. The base class DbContext has functions to create and delete the database as well as to check for its existence.

I want to check if a special table (entity) is existing or not. Is it possible with an framework implementation or do I need to write custom methods? If I need to write my own implementation, what would be the most generic approach to do that?

Thanks for any help.

Upvotes: 28

Views: 50463

Answers (8)

Tyler Jones
Tyler Jones

Reputation: 1333

Here's an extension method for doing this in EF Core (without Dapper):

public static async Task<bool> TableExists(this DbContext context, string tableName)
{
    var connection = (SqlConnection)context.Database.GetDbConnection();
    if (connection.State != ConnectionState.Open)
    {
        await connection.OpenAsync();
    }

    await using var command = connection.CreateCommand();
    command.CommandText = $"SELECT COUNT(*) FROM sys.tables WHERE name = '{tableName}'";
    var result = await command.ExecuteScalarAsync();
    var count = (int)result;
    return count > 0;
}

Upvotes: 1

Sina
Sina

Reputation: 49

this code create all tables automatic if dose not exist

 protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            var x = modelBuilder.RegisterEntityType;
        }

Upvotes: -2

Miti Razvan
Miti Razvan

Reputation: 31

In EF Core, I have added the TableExists method as a extension method for the DbContext class. Here is my solution using Dapper.

using System.Linq;
using Dapper;
using Microsoft.EntityFrameworkCore;

public static class DbContextsExtensions
{
    public static bool TableExists(this DbContext dbContext, string tableName)
    {
        var sqlQ = $"SELECT COUNT(*) as Count FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = '{tableName}'";

        var conn = dbContext.Database.GetDbConnection();
        {
            if (conn != null)
            {
                // Query - method extension provided by Dapper library
                var count = conn.Query<int>(sqlQ).FirstOrDefault();

                return (count > 0);                    
            }
        }
        return false;
    }
}

And here is an usage example:

if(context != null && context.TableExists("AppSettings"))
{
   // do something;
}

Hope this help other people.

Upvotes: 3

philu
philu

Reputation: 874

An alternative method; it's not as efficient as Ladislav's, but it's not tied to SQL Server (edited to add Where clause to address performance issue):

bool CheckTableExists()
{
    try
    {
        context.YourTable.Where(s => s.<yourKeyField> = <impossible value>).Count();
        return true;
    }
    catch (Exception)
    {
        return false;
    }
}

Upvotes: 4

Ali Soltani
Ali Soltani

Reputation: 9927

I think following code is a little bit more understandable.

using(YourDbEntities db = new YourDbEntities()) 
{
  bool IsExists = db.Database
   .SqlQuery <int?> (@"
    SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES 
    WHERE TABLE_NAME = '" + yourTableName + "'
    ")
    .FirstOrDefault() > 0;

    return IsExists;
}

Upvotes: 2

Aaron Hudon
Aaron Hudon

Reputation: 5839

Assumption: SQL Server

Catching any old exception when querying the DbSet does not mean the table does not exist.

Querying a DbSet where the table does not exist will throw an EntityCommandExecutionException with an inner exception of type SqlException. That inner exception has an ErrorNumber property.

Error number 208 reads (source):

Invalid object name '%.*ls'.

Upvotes: 2

Dmitrii Polianskii
Dmitrii Polianskii

Reputation: 575

I can't add comment to previous post. I'm using SQL Compact and I don't know schema of the table. I'm using this code to check for table It's pretty the same that in previous post but It works for any table.

    /// <summary>
    /// Check if data table is exist in application
    /// </summary>
    /// <typeparam name="T">Class of data table to check</typeparam>
    /// <param name="db">DB Object</param>
    public static bool CheckTableExists<T>(this ModelLocker db) where T : class
    {
        try
        {
            db.Set<T>().Count();
            return true;

        }
        catch (Exception)
        {
            return false;
        }
    }

Upvotes: 6

Ladislav Mrnka
Ladislav Mrnka

Reputation: 364249

If you need to check existence of the table you must call custom SQL code:

bool exists = context.Database
                     .SqlQuery<int?>(@"
                         SELECT 1 FROM sys.tables AS T
                         INNER JOIN sys.schemas AS S ON T.schema_id = S.schema_id
                         WHERE S.Name = 'SchemaName' AND T.Name = 'TableName'")
                     .SingleOrDefault() != null;

Table name is defined by default as the name of DbSet exposed on your derived context but the default name can be overriden either by fluent API's ToTable method or Table data annotation.

Doing this in the generic way is not something supposed in code first approach. That will require browsing metadata and manually explore to which table is the entity mapped - this can be pretty complex because entity can be mapped to multiple tables. Code first doesn't offer access to metadata. You must convert DbContext to ObjectContext and browse MetadataWorkspace.

Edit:

To convert DbContext to ObjectContext use this:

ObjectContext objContext = ((IObjectContextAdapter)dbContext).ObjectContext;

Upvotes: 43

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